I am going Elk Hunting tonite and need information please..


My 95 GMC 4x4 6.5 "s" threw 3 codes last night. I was accelerating uphill when the SES light came on. Code 15, 33,34 . My Haynes manual tells me that 15- Engine coolant temp sensor circuit, Low temperature. 33- EGR sensor low vacuum, 34 ignition timing stepper motor fault.


Truck has a new vacuum pump 2 weeks, but when I bought the proper one for the 95 with air conditioning the pulley did not fit on new pump. I ended up with a non-air conditioned one and it fit. Apparently the pulleys are different shaft sized to prevent the wrong one from being installed as the non air conditioned one runs opposite direction from the air conditioned one. Here's the kicker the truck had a complete rebuild prior to me buying it ($7700.00) Was the wrong pump put on the motor, and is this causing me trouble? Vacuum pump has the proper vacuum at idle (check with information from other posts I believe 25" at pump and 15" at wastegate at idle) but when I load up the truck if the vacuum pump is running backwards could it be losing vacuum? Truck runs good, idles good, has never stalled, and gets excellent fuel economy (compared to my cummins 600)


Thanks in advance and help appreciated. Dan Edited by: steelydan

Anyone?

I don't but I bet others will be here shortly and they will know

Dan,


If the pump makes vacuum it makes vacuum.


EGR vacuum low could be a faulty EGR diaphram. Check the EGR to see if it holds pressure. Make sure the CTS has voltage, wiring could be faulty or intermittent. CTS fault would throw TSM off. It would fully advance it to 14*. I've seen this. The wiring can become a tangle ontop of the block and it's hot and moving up there. The wires can become brittle and connection intermittent.


Check it out, I'd like to hear back on it.

temp sensor controls fuel for cold starts, like a choke to get more fuel when cold. if that is out of wack it could cause other codes and problems. those temp sensors tend to break and when they show wide open the truck doesn't think its warming up so it keeps dumping fuel. being that your code is for low temp i would check the wiring to the sensor then replace the sensor.

QM, I checked the egr it holds vacuum o.k.


Lupey6.5 I assume the temp sensor is the one directly under the alternator? Driver side front of the head? The temperature guage in the truck never gets above 180.. Is there a way to check the sensor? I have a pyrometer to verify casting temp.. do you know what resistance = what temp?


Thanks Dan

i don't know the resistances but the sensor you are looking at is for the dash indicator(gauge)-- the sensor that talks to the ecm is up top on your water crossover.

180*F might indicate the time for a new thermastat has come. They cost a few dollars with the gasket, that's cheap insurance.


The Tempature to resistance is in any service manual. I listed the entire table on an old post but I'll give you a few for an idea.


30*C-86*F = 2796 ohms


20*C-68*F = 3520 ohms


15*C-59*F = 4450 ohms


10*C-50*F = 5670 ohms


5*C-41*F = 7280 ohms


0*C-32*F = 9420 ohms

Can I switch the temp sensor from the block to the water outlet and see if the problem goes away or are they different? They appear to be the same thread size.


Dan

I think what's importantant is how many ohms resistance it's showing vs. engine coolant tempature.

Thanks for the information I will get a new sensor..... Dan

when i needed a new sensor for the water jacket because i broke the plastic plug off the dealer told me both the sensor in the water jacket and on the block where the same part #. I'd check first before spending any $$$ because the one on the head only has 1 wire going to it but the one on the crossover has 2.

Finally got time to install a new coolant sensor. When I traced the wires checking for a loose connection prior to ordering a new sensor I found that the previous owner had cut the wires at the sensor, and wired in a switch under the dash for cold starting.(he told me that he flips the switch in cold weather to facilitate eay starting and then flips it back) The switch increased the idle speed. There was 3 wires on the switch. Common NO and NC. Although there was 3 wires wired all the way to the sensor, only 2, Common and NO were used. Actually worked well and truck started good when cold. I disconnected the switch, and installed a new coolant sensor. It has 2 wires on it. I would think that all the switch did was disconnect the sensor from the ecm to trick it to think it was colder that it really is and allow it to add more fuel for starting.. or am I out in left field?


The sensor also has 2 wires on it. Does the ECM read continuity between the 2 wires or is there 2 separate circuits and they are reading continuity to ground? Thanks in advance Dan..

5v signal comes in from VCM pin RE23 wire 410 yel, is resisted by the sensor to reflect ECT and goes to VCM ground pin gr4 on 452 blk.