Engine code P0236
When I check the freeze frame I get the following information
Calc load% 87.45
ECT (deg F) 188
Engine RPM 2025
Veh Speed (MPH) 47
IAT (deg F) 91
Calc Load % 87.45
Can anyone dell me if this narrows the cause of the error code. I will get this code and sometimes it sets the check engine light & some times it doesn't. If I leave it (don't erase) the engine light will go out and it won't display an error code.

Thanx in advance
Joe

I didn't look up the code, but I think 0236 is "boost out of range".

The freeze frame says you were working the engine pretty hard at the time, and there was either too much or too little boost -- or the computer "saw" too much or too little boost. It's too bad the freeze frame doesn't store that data. With the complexity of the stupid boost system, it's usually too little boost that sets the code. If you go a certain number of starts without setting the code, the light will go out. With mine, if I whack the solenoid with a screwdriver, it works fine. With intermittent problem like that, I'd suspect the solenoid, though your sig says yours is new.

...or maybe it's overboost. Stupid freeze frame. ...not very helpful. What was the outside air temp at the time? Your computer is seeing 91 degrees IAT, so if it was warm outside, then it's more likely you gots no boost.

I ran that through the DTC lookup on the site and here's what it says:

DTC Information
Code: P0236
Modules:
Description: Turbocharger Boost Sensor A Circuit Range/Performance

Did you do any turbo related work lately?

You were working the engine pretty hard at the time, and there was either too much or too little boost -- or the computer "saw" too much or too little boost. It's too bad the freeze frame doesn't store that data. With the complexity of the stupid boost system, it's usually too little boost that sets the code.

I didn't look up the code, but I think 0236 is "boost out of range".

My reader shows "Turbo/supercharger boost sensor A circuit range/performance

I am not sure what you mean by the freeze frame storing the data. It will give me one error that doesn't set check engine light and the next instance sets the light.
my reader saves the freeze frames & I have saved a couple on my computer at work, if that would help

& you are right I was comming on to it a bit at the time:o:

I ran that through the DTC lookup on the site and here's what it says:

DTC Information
Code: P0236
Modules:
Description: Turbocharger Boost Sensor A Circuit Range/Performance

Did you do any turbo related work lately?

No turbo work lately other than i found and fixed a leak in the line at the WG actuator

The vehicle seems to run quite well. I really have no other problems(as yet). If I install a boost gauge & manual WG adjust , is there some graph, spreadsheet etc to compare pressure to rpm. TWISI unless the gauge shows no boost or pins out at over boost how do I know how much boost to use a specified time?

if he had low boost the EGT's would be high and so the IAT's. However if the boost was too high it could also cause high EGTs and thus high IAT's. However his IAT's seem fine to me.

With 87% load, 2000 rpm, 47 mph, coolant up to temp, and a IAT of 91 degrees, you are either not getting enough boost. That intake air temp is pretty low from what I see, especially with it warmed up.

Throw a boost gauge on it, and let us know what the manifold pressure is when it codes.

Throw a boost gauge on it, and let us know what the manifold pressure is when it codes.

Thank you. That shall be my next project. might take a couple of weeks though. Just did remote PMD:thumb: for $700+ so am kinda short right now:(

my boost gauge cost me $30 so it isnt a HUGE expense...

My reader shows "Turbo/supercharger boost sensor A circuit range/performance

I am not sure what you mean by the freeze frame storing the data. It will give me one error that doesn't set check engine light and the next instance sets the light.
my reader saves the freeze frames & I have saved a couple on my computer at work, if that would help

& you are right I was comming on to it a bit at the time:o:

I just meant it's too bad the freeze frame doesn't store boost readings. That would be most helpful. The ECM decides how much boost is necessary based on variable conditions. For example, at 5000 ft elevation here, my ECM calls for, and is happy with, upwards of 12 psi or better. At lower altitudes, it would set a code with that much boost. It'd also be nice if the freeze frame would say how much boost the ECM was expecting.

As for it only setting the light sometimes, there are parameters for the light vs parameters for storing the code. My book is outside in my truck right now, and I'm too lazy to go look it up.

If I hadda guess, I'd guess your ECM was seeing less boost than it wanted, but that's just a guess based on the IAT and how hard you were working the engine at the time. ...could also be a flaky MAP sensor giving the ECM bad input. ...or some loose wiring, not necessarily always a sensor problem. ...but if you had boost, I'd expect to see the IAT higher.

I just meant it's too bad the freeze frame doesn't store boost readings. That would be most helpful. The ECM decides how much boost is necessary based on variable conditions. For example, at 5000 ft elevation here, my ECM calls for, and is happy with, upwards of 12 psi or better. At lower altitudes, it would set a code with that much boost. It'd also be nice if the freeze frame would say how much boost the ECM was expecting. Damn!! I think i might be starting to understand some of this:thumb:

As for it only setting the light sometimes, there are parameters for the light vs parameters for storing the code. My book is outside in my truck right now, and I'm too lazy to go look it up.
If I am correct the first setting doesn't set the engine light but if it happens twice in a row the check engine light comes on. It will go off on its own if there are no subequent occurances in the next trip

If I hadda guess, I'd guess your ECM was seeing less boost than it wanted, but that's just a guess based on the IAT and how hard you were working the engine at the time. ...could also be a flaky MAP sensor giving the ECM bad input. ...or some loose wiring, not necessarily always a sensor problem. ...but if you had boost, I'd expect to see the IAT higher.

Thank You
This has been an enjoyable learning experience for me.

Have a grand life
Joe

I hate to say it, but ignore what Torque454 said. Low boost will cause low intake air temperature, not high. High turbo boost = higher temp, hence the reason for intercooling. When you compress air, it heats up. Low boost can cause high exhaust temps though, but not high intake temp.

Hello, low boost = High EGT. That causes the hot side of the turbocharger to be hotter, which transfers to the "cold" side. Intercoolers are needed for that reason, also. Heat transfer from turbine side to compressor side is probably where the majority of the heat comes from anyways. I am NOT saying he doesnt have low boost, obviously there is a boost problem or that code would not be set. I am however saying that i personally dont believe low IAT = low boost. How else does the computer know to cut the fuel rate on hills and things? It measures the IAT's. That heat comes from the hot side of the turbo.

Hello, low boost = High EGT. That causes the hot side of the turbocharger to be hotter, which transfers to the "cold" side. Intercoolers are needed for that reason, also. Heat transfer from turbine side to compressor side is probably where the majority of the heat comes from anyways. I am NOT saying he doesnt have low boost, obviously there is a boost problem or that code would not be set. I am however saying that i personally dont believe low IAT = low boost. How else does the computer know to cut the fuel rate on hills and things? It measures the IAT's. That heat comes from the hot side of the turbo.

I wasn't going to comment on the earlier post, but I thought maybe you confused the ECT in the freeze frame with the EGT you mentioned earlier. The ECM knows nothing about EGT, just like you imply in this post.

However, I question the statement I highlighted in red. Basic gas laws dictate that when you compress a gas, the temperature goes up -- and goes up instantly. PV/T=PV/T. That's a linear relationship, so if you double the pressure with the container volume being constant, you could expect roughly double the temperature.

What you mention about the high EGT could explain a slightly higher IAT than normal at atmospheric pressure. According to the data, the truck should have been pretty much into full boost (whatever the ECM decided that was) and the IAT should be higher. Assuming the ECM was calling for 12 psi at the time, that would raise IAT significantly (and instantly) just by compressing the air. I don't know what it should be (my freshman chem class was 25 years ago), but I would think close to double the ambient temp wouldn't be out of line. That's ambient temp at the sensor, not necessarily outside air temp. Add hot underhood temps to the equation, and it seems that 91 degrees isn't high enough to say there was much boost going on.

I think you have the right idea, but are coming to the wrong conclusion about temperature and boost -- or perhaps you're coming to the right conclusion and I'm just misreading your post. High boost conditions must always cause high IAT (unless the charge is cooled by a non-factory add-on of some sort), and cause it instantly -- basic chemistry (or physics). Low IAT implies less boost. Excessive IAT indicates too much boost, or with your explantion, too much EGT, so if the IAT is too high, the ECM will cut fuel. Whether it's from boost or external heat, the ECM will cut fuel for a high IAT, not a low one.

Your explanation of the heat transfer from EGT could help explain that the ambient temp seen by the IAT sensor could be higher than normal at atmospheric pressure, not lower. However, the gas laws (Boyle, et al) dictate that higher pressure will always cause higher IAT in the absence of an external cooling device.

Just to throw yet another variable in, there's also the possibility that the IAT sensor cannot react quickly enough to temperature change to instantly detect the instantaneous rise in temperature caused by boost. It sure would be nice if the freeze frame would record the boost level, then we'd have the answer.

glossary of acronyms as I understand them:
IAT = Intake Air Temperature -- monitored by probe in intake manifold.
EGT = Exhaust Gas Temperature -- not monitored
ECT = Engine Coolant Temperature -- monitored by a probe in the head (or is it the other probe?)
ECM = Engine Control Module (computer) -- does the monitoring

Hello, low boost = High EGT. That causes the hot side of the turbocharger to be hotter, which transfers to the "cold" side. Intercoolers are needed for that reason, also. Heat transfer from turbine side to compressor side is probably where the majority of the heat comes from anyways. I am NOT saying he doesnt have low boost, obviously there is a boost problem or that code would not be set. I am however saying that i personally dont believe low IAT = low boost. How else does the computer know to cut the fuel rate on hills and things? It measures the IAT's. That heat comes from the hot side of the turbo.

No. The Ideal Gas Law (Pv=nRT) will tell you everything that you need to know regarding the source of IAT's. Compressing the air (P goes up) causes the temperature to rise (T goes up to balance the equation). Throw in a compressor with lousy efficiency above a 1.7 pressure ratio and you have the recipe for really high IAT's at boost levels above ~10psi. Please also remember that GM had to meet "emissions" as they were back in the day and limiting the IAT's was one way to help meet that. I guess that a CAC was too expensive to utilize...:rolleyes:

The oil flowing through the center section of the turbo effectively thermally isolates the compressor from the exhaust side.

Regards,

I had posted code results earlier (& will post them again here for comparison)
old code 236 New code 236
Calc load% 87.45 0.00
ECT (deg F) 188 -40
Engine RPM 2025 0
Veh Speed (MPH) 47 0
IAT (deg F) 91 -40
NOW. I was traveling about 30Km/H. I was not accelerating hard. The ambient temp was about 36 F. Sorry still no boost gauge yet. Again the truck seems to run quite well & I don't notice any change at the time it throws the codes other than the check engine light or the reader. How can this happen when the engine isn't running & I was driving?:rolleyes:

Thanx for any response
Joe

OOPS The new codes in my last post were pending codes & not freeze frame, if that helps any.

No. The Ideal Gas Law (Pv=nRT) will tell you everything that you need to know regarding the source of IAT's. Compressing the air (P goes up) causes the temperature to rise (T goes up to balance the equation). Throw in a compressor with lousy efficiency above a 1.7 pressure ratio and you have the recipe for really high IAT's at boost levels above ~10psi. Please also remember that GM had to meet "emissions" as they were back in the day and limiting the IAT's was one way to help meet that. I guess that a CAC was too expensive to utilize...:rolleyes:

The oil flowing through the center section of the turbo effectively thermally isolates the compressor from the exhaust side.

Regards,

If heat could not be transferred from the hot side to the cold side of the compressor, IAT's would NEVER get too high. The factory system wouldn't allow enough boost for that. My boost doesnt go over 8psi and i still will defuel on hills. That defuel is from high IAT. The only explanation? Transfer of heat from the turbine side. Im not going to say either of you are wrong, but thinking logically either low or high boost condition could cause a high IAT. If the turbo did not work at all, the EGT's would be even hotter (thus the hotside of the turbo would be hotter) but the engine is still sucking air from inside a hot turbocharger. I'm not saying heat isnt coming from the compression of the air - it does. Thats how a diesel engine runs. I am saying tho that i can see either high or low boost causing a high IAT. High IAT is not the problem here, but my point is either condion (high/low boost) can cause either high or low IAT. While you may be correct, MOST of the time a low IAT may be indication of low boost, i do beleive it can be the other way around, too. I just tend to look alot deeper into things than most people do. Sorry, but thats how I am. It makes me a pain in the ass sometimes, but i see stuff that sometimes normally wouldnt be seen otherwise.

. It makes me a pain in the ass sometimes, but i see stuff that sometimes normally wouldnt be seen otherwise.

Thanx for the info.
& sometimes, being a pain in the ass is the only way to get noticed

Thanx again
Joe

If heat could not be transferred from the hot side to the cold side of the compressor, IAT's would NEVER get too high. The factory system wouldn't allow enough boost for that. My boost doesnt go over 8psi and i still will defuel on hills. That defuel is from high IAT. The only explanation? Transfer of heat from the turbine side. Im not going to say either of you are wrong, but thinking logically either low or high boost condition could cause a high IAT. If the turbo did not work at all, the EGT's would be even hotter (thus the hotside of the turbo would be hotter) but the engine is still sucking air from inside a hot turbocharger. I'm not saying heat isnt coming from the compression of the air - it does. Thats how a diesel engine runs. I am saying tho that i can see either high or low boost causing a high IAT. High IAT is not the problem here, but my point is either condion (high/low boost) can cause either high or low IAT. While you may be correct, MOST of the time a low IAT may be indication of low boost, i do beleive it can be the other way around, too. I just tend to look alot deeper into things than most people do. Sorry, but thats how I am. It makes me a pain in the ass sometimes, but i see stuff that sometimes normally wouldnt be seen otherwise.

From a heat transfer point, your premise does not hold water. To get exhaust heat to be raising IAT's to that level, because of the temperature gradient effect, you would have to have the center section of the turbo at greater than 350 deg F, this would cook the bearings and oil in no time at all. A trashed turbo would result.

I certainly don't won't to come off as thwarting innovative or "out of the box" thinking. There may be SOME influence on IAT's, but it is very slight. Sometimes to be truly innovative in your thinking, you have to know why the box exists in the first place.

I highly doubt that GM is looking to IAT's as a means of gauging EGT's and therefore judging when to cut-back power.

Also be aware that since the 6.5TD is "actively" managing the boost pressure (within a certain range) using exhaust gas control, there other factors that could cause high IAT's. Excessive intake restriction while trying to produce target boost would cause the compressor to operate at a pressure ratio higher than "normally" required. This can cause high IAT's. Same goes for leaks in the boost pressure side of the turbo system. In both cases, the W/G would be "clamp down" in an attempt to increase boost into the "target range". This causes the compressor to wander into higher pressure ratio territory (and lower efficiency ranges) and could result in higher (than normal) IAT's for a given boost.

Regards,

Engine code P0236
When I check the freeze frame I get the following information
Calc load% 87.45
ECT (deg F) 188
Engine RPM 2025
Veh Speed (MPH) 47
IAT (deg F) 91
Calc Load % 87.45
Can anyone dell me if this narrows the cause of the error code. I will get this code and sometimes it sets the check engine light & some times it doesn't. If I leave it (don't erase) the engine light will go out and it won't display an error code.

Thanx in advance
Joe

What sort of device are you using to collect that "freeze frame" data?

What you need to know is the waste gate duty cycle commanded by the PCM and the corresponding boost pressure to see if you are out of range on the high or low side.

Generally low boost is the most common problem, low vacuum, caused by failing vac pump, cracked lines, faulty waste gate solenoid, etc.

Back when I was still running the vacuum pump, I replaced the
turbo boost sensor and fixed the code you have. But you need to check vacuum at the pump, at the sensor, and at the wastegate solenoid.
Any bad vacuum hoses or solenoids could cause that code to pop up.

What sort of device are you using to collect that "freeze frame" data?



I am using a CanOBD2 code reader 3100. (I think it is made by INNOVA)

Back when I was still running the vacuum pump, I replaced the Turbo boost sensor

& where might I find that or is that another name for the WG solinoid

I hate to hijack this thread to something else, but I hate seeing someone having the wrong idea.

Torque, your system would defuel not because IAT was high, but boost was too high for too long. The ECM monitors the manifold pressure from the manifold air pressure sensor. If this is too high for too long, or the intake air temp is too high, the system will defuel and throttle back. Intake air temp and pressure go hand in hand. I can chill the air to -30 and have the system defuel at less than 12 psi.

Heat does transfer from the hot side to the cold, but not that much. If you run a turbo from high volume compressed air, you'd be supprised how much heat comes from compressing air, even at 10 psi. At 80 degrees outside temp, you wouldn't want to hold onto it. Trust me. I've done it. Feel an air compressor that compresses air to 100 psi. The one at our shop reaches a head temp of over 200 degrees, and it has a cooler to remove heat. Take an air line with 30 psi wide open, and see how cold it gets. Same thing, only the opposite direction. Decompressing air makes it colder.

Enough on that. If you don't believe us, read around, and you'll find info on this subject.

http://www.howstuffworks.com/turbo.htm

Quote from above link:

"In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds of up to 150,000 rotations per minute (rpm) -- that's about 30 times faster than most car engines can go. And since it is hooked up to the exhaust, the temperatures in the turbine are also very high."

Why then, if everything is so hot, do I get ECT at Minus 40 Degrees and IAT of Minus 40 Degrees

Why then, if everything is so hot, do I get ECT at Minus 40 Degrees and IAT of Minus 40 Degrees

sensors inop or unplugged, bad wires open connection/circuit. -40 is what the ECT sensor sees if the ECT is unplugged.

sensors inop or unplugged, bad wires open connection/circuit. -40 is what the ECT sensor sees if the ECT is unplugged.

Thank you very much. it DOES narrow it down for me

Thanx again
Joe

sensors inop or unplugged, bad wires open connection/circuit. -40 is what the ECT sensor sees if the ECT is unplugged.

That's correct. But why all of a sudden is the ECT not working. In his first post the ECT reading was 188 degrees and the IAT. Now it shows -40. There may be an intermittent problem, and/or perhaps a bad ground. Which could also cause his P0236 code also.

That's correct. But why all of a sudden is the ECT not working. In his first post the ECT reading was 188 degrees and the IAT. Now it shows -40. There may be an intermittent problem, and/or perhaps a bad ground. Which could also cause his P0236 code also.

The problem is very intermittent. There is no rhyme or reason as to when it happens.hot/cold, accelerating/braking, highway/city etc,etc. It could at any time. some times the codes disappear right away & sometimes not. It may not happen for 15 to 20 trips and then happen 2-4 times in one day.
I'll check wires in the morning. It does seem that the pending code shows 0 degrees whereas the freeze frame will show a higher temp as in my first post

Thanx
Joe

Grounds are always suspect on these engines. It would be the first thing to check (IMHO). A chaffed or broken wire (contacting intermittently). Pins and clips in factory connectors not making proper contact (expanded clips or corrosion). The wires on the WG solenoid are know to break in/under the insulation.

Joe would you mind filling out your signature with all your trucks info and what upgrades you have done. You can do it through this link.


http://www.dieselplace.com/forum/profile.php?do=editsignature

Joe would you mind filling out your signature with all your trucks info and what upgrades you have done.

Sorry. I have already done that , I just didn't show it when I replied to my own or anothers post:o:

How's this?

I have no idea what year your truck is Joe, but on the '95 (according to the schematic I have) the ECT Common wire (ECT pin D6) is black and is on a circuit to the ECM shared by the MAP sensor, CPS, EGR control/Baro sensor, and IAT sensor. - Nothing to ground.
The signal (actually, a changing resistance) to the ECM is the yellow wire.
Just a guess, but I believe 1 of/or 3 possibilities exists.
The ECT is bad, the plug to the ECT is corroded and not making connection, or one of the two wires is broke. Could even be broken under the insulation which you can usually find by gently flexing the wire along it's length - If it's broken somewhere you'll know when you find it. Best bet for a broken wire is at a connector or solder joint, if there are any. Next best is where the wire takes a sharp bend.
It IS possible that the sensor itself has something loose in it, but sudden erratic readings can usually be traced to a corroded connection, solder joint, or wire.
Good Luck...
It would help if you would fill out your signature (http://www.dieselplace.com/forum/profile.php?do=editsignature). It helps to know what year, etc the truck is to find the correct schematic - Mine is for an OBD-1 control system.

On edit... Right when I posted this your signature came up - cool - Your's is an OBD-2 system, so the pin numbers and wire colors could be different.

Thanx a bunch to ALL of you dieselheads who answered my post, even if it did cause some opposing answers amongst yourselves. If any of you enjoyed or got even a little of knowledge from this thread, it was all worth it for all.
As for me I do believe that i have a great deal of information to digest but am definatly on the right track, thanx to all of you. I will start with checking wires & connections (cheapest), Then boost gauge( a little more)(see where I am going with this?):D
Again, Thanx to the whole forum. There is a lot of great reading & help here. If I ever get fired or divorced AGAIN;) It will be because I have been reading this forum.:o::thumb:

Thanx again till my next problem;)
Joe

How's this?

Thats great now we don't have to go back to the OP to remember what you have.

http://www.howstuffworks.com/turbo.htm

Quote from above link:

"In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds of up to 150,000 rotations per minute (rpm) -- that's about 30 times faster than most car engines can go. And since it is hooked up to the exhaust, the temperatures in the turbine are also very high."

Since we're provding meaningless quotes:

[From Hershey Candy commercial (formerly from Peter Paul Company)]: "Sometimes you feel like a nut, sometimes you don't"

Your quote provides no useful information to your previous argument, much the same way mine does not. I believe that 99% of the forum members here understand that the temperatures "in" the turbine would get very hot. Most people with pyrometers would tell you that they approach 1200 deg F (or higher...:eek:).

Regards,

May be IAT sensor is faulty?