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6.5L Diesel Engine Discuss the 6.5 GM diesel engine & associated components. Automatic transmission questions & problems belong in the 4L80/85 - 4L60E - 6L90 Transmission Forum

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Old 02-03-2009, 10:02 PM   #1 (permalink)
BlueBurby1
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Boost Control Diagnostics

P0236-P0238 Diagnostics
BlueBurby1
A little background info on these codes:

These codes are in regards to the boost control circuit on 6.5TD built with OBD-II Capability.

Overboost, Underboost, and non responsive units will all set these codes.
To test the system follow these steps, and then post back with results.
This will work for F code engines, for S code the steps are the same, but you need to trace the EGR vacuum lines to ensure there are no leaks.

P0236 = Boost is 20 kPa or 2.9 PSI from PCM expectations at 1800-2400 RPM, under load.

P0237 = Boost is under 40 kPa or 5.8 PSI

P0238 = Boost is equal to or greater than 202 kPa Under 3506 RPM.

1. Check all battery connections and grounds. This is important as the PCM can do all kinds of weird things without proper grounding.
ENGINE OFF
2. Check that you can freely move the waste gate actuator (mounted on the turbo with a vacuum line running to it)(remove vacuum line and move actuator while placing your finger over the vacuum port, you should be able to get suction and pressure)if you get no pressure/vacuum playing with the actuator, replace actuator.
3. Check the vacuum line running from the actuator to the solenoid(driver side of engine near intake manifold...has two vacuum lines, check these lines for any cracks or breaks, but be careful, itís easy to snap them(in which case repair any vacuum lines as necessary).
4. Follow the vacuum line back to the vacuum pump, with the Belt off, see if you can turn the vacuum pump, you should feel resistance due to the pumping action. Also feel for grinding...any grinding or lack of pumping, suspect unit.
ENGINE RUNNING(belt replaced and hoses reconnected)
5. Check for vacuum at the solenoid. If you have no vacuum AT the solenoid and the vacuum line is good. Replace vacuum pump.
7. Check for vacuum coming OUT of solenoid(solenoid should activate and buzz when truck is idling)if no vacuum or solenoid not functioning. Replace solenoid.
8. Check for vacuum at actuator, if no vacuum at actuator, recheck vacuum lines.

Your MAP Sensor may be at fault, and is cheaper than the PCM. If mechanically/pressure wise everything is A-OK, Replace the MAP Sensor. NOTE:The Diesel MAP Sensor is different from the Gas MAP Sensor.

9. If you STILL canít get the system working, the problem may be the PCM. Find a test unit(spare PCM) OR Order a Heath GL-4 and Turbo-Master(if you choose to upgrade, if you want to leave stock or have thrown a ton of parts at it...just get the GL-4/or a factory PCM)

This is just a guide, and you should post back your testing results BEFORE purchasing and replacing parts...we will help you along, and I hope you enjoyed reading my guide

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Last edited by BlueBurby1; 10-02-2011 at 08:51 PM.
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Old 10-02-2011, 08:54 PM   #2 (permalink)
BlueBurby1
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I have updated this diagnostic and am looking for input on making it better.

this was brought to my attention by a recurring 236 code on my own truck.

Be aware that this thread will be locked again on OCT 7th, 2011 and changes made to the diagnostic as necessary.

Please keep comments on topic otherwise the thread will be cleaned and locked early.

Thank you for your input in advance

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DIAGNOSTIC HELP CLICK HERE
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For Members with vehicles with PassLock or PassKey Security issues. PM for details on "Fixing" this system.
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Old 07-07-2015, 06:08 PM   #3 (permalink)
mikeyG
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Hey I just got this code, and I'm curious as to why.

My OD drops out so I had to hit a hill going 2500 rpm in 3rd gear, could this cause it?

Everything checks out correct.

I had broken a vac line a month ago and decided to directly attach the vacuum to the waste gate actuator, completely bypassing the solenoid. Could this be the cause? By directly attaching the vac like to the actuator, does that create max boost or?

I suppose: what does the solenoid actually do?


Cleared the codes and truck runs perfect now.
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Old 07-08-2015, 08:10 AM   #4 (permalink)
jimrig
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yes that would make sure your wastegate stays closed all the time. The solenoid is controlled by the PCM. Your boost sensor, PCM, and wastgate solenoid work together as a system by managing your boost under all throttle conditions. By bypassing the solenoid you are creating a situation where the PCM has no control over the boost level and will try and protect the engine by setting a code and going into a "limp Mode". Before I made my own wastegate controller I did the same thing and bypassed the solenoid and was getting 20+lbs of boost just from the vacuum pump. I also left my solenoid connected so the PCM would sense that it was still attached. If you have a stock programmed PCM if it sees anything over 12psi for more than 5seconds if I remember right it will set a code.
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Old 07-26-2015, 12:19 PM   #5 (permalink)
mikeyG
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Thanks! Another question:

I have vacuum line to re install the solenoid, but I now don't know which is the intake and outtake vacuum lines at the solenoid, does the vacuum go to the front most solenoid hole, and then the rear most solenoid hole to the waste gate?
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Old 07-26-2015, 12:24 PM   #6 (permalink)
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Quote:
Originally Posted by mikeyG View Post
Thanks! Another question:
does the vacuum go to the front most solenoid hole, and then the rear most solenoid hole to the waste gate?
Yes..
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