Dtc 14

[greg2010]

DTC 14

Hey guys, I've got a 1994 C1500 with the 6.5 Turbo in it. I love the truck, but for the past little while the check engine light has been coming on. I used a paper clip in the Diagnostic Link to pull the codes and it's flashing only code 14--Engine coolant temp sensor error (high temp indicated). Problem is, the light is on virtually all the time (even when it's below 0 degress out and the truck has sat out all night), though if I accelerate hard, the light often goes out. There is no visible smoke at any time or through any RPM range, and the engine is not sputtering or doing anything out of the ordinary.

My engine appears to have 2 coolant temperature sensors. There is one in the cylinder head that appears to be powering the temp gauge on the dash, and there is a second temp sensor by the thermostat that appears to be in charge of the idle. I remove the one at the water neck with the engine running and the RPM increases, with no change to the dash gauge. When I remove the one in the head, the dash gauge changes.

Any thoughts as to where I should start to look?

Thanks everyone!
~Greg. :)

[Chevylover]

DTC 14

Hey guys, I've got a 1994 C1500 with the 6.5 Turbo in it. I love the truck, but for the past little while the check engine light has been coming on. I used a paper clip in the Diagnostic Link to pull the codes and it's flashing only code 14--Engine coolant temp sensor error (high temp indicated). Problem is, the light is on virtually all the time (even when it's below 0 degress out and the truck has sat out all night), though if I accelerate hard, the light often goes out. There is no visible smoke at any time or through any RPM range, and the engine is not sputtering or doing anything out of the ordinary.

My engine appears to have 2 coolant temperature sensors. There is one in the cylinder head that appears to be powering the temp gauge on the dash, and there is a second temp sensor by the thermostat that appears to be in charge of the idle. I remove the one at the water neck with the engine running and the RPM increases, with no change to the dash gauge. When I remove the one in the head, the dash gauge changes.

Any thoughts as to where I should start to look?

Thanks everyone!
~Greg. :)


One sensor is for dash gauge and one is for the ECM.

In my opinion you should first clear (remove the battery cables for about 15 min.) the code and wait to see if the code come again. If not -> problem solved. If the code comes back, i would rplace the sensor which give the signal to the ECM - should be the one at the water neck. Clear codes again, see if the code comes back. I think this could be the only way.

Cu,
Sven

[christja]

You can also clear the codes by holding down the break and fuel for 15 sec while in diagnostic mode with the paper clip in. per Walt.

"# Q: How do I read my DTC (Diagnostic Trouble Codes) on my 94-95 truck??
# A: Locate the "Data Link" connector below the steering wheel on the rim of the dash. With the key in the "OFF" position, jumper the top two right terminal pins (termnals A&B) with a paperclip or short piece of wire. Turn the key to the "RUN" position, but DO NOT START. The check engine light will begin flashing a sequence of codes. If the diagnostics are working and there are no codes in memory, a code 12 will flash 3 times. A code 12 is a flash once, followed by a quick flash two times. Basically a 1-2 flash is a code 12. If no codes, only the 12 will flash. If codes present, the sequence will start with the 12, then flash each code 3 times before moving onto the next in numerical order. When 12 flashes again, you are done. Again, count the flashes and write them down, they will flash 3 times each code. To clear the codes, depress the brake pedel and accelerator pedel simultaniously for 15 seconds while still in diagnostic mode. NOW shut off the key and remove the jumper. The codes are now cleared. NEVER-EVER remove the jumper while still in the diagnostic mode, turn key to off first. NEVER-EVER start the truck with the jumper in place. ECM damage may result. Let me know the code numbers that came up along with symptoms and I will help you diagnose your truck. "

[sixnickel]

I would replace the sensor in the water manifold thats is the one for the ECM. It's gone bad and it's telling the ECM the engine is hot. I would think you might be also having a short glow plug cycle? When you unplug it it thinks the engine is cold and goes into high idle and cold advance. The part #for SSDiesel Supply is SSD-052 for that sensor. Good Luck!

[greg2010]

Thanks for the info. Indeed, the glow plug cycle is shorter with the sensor connected, thouogh it's only shorter by about 1 second. Though I do notice that the truck is more difficult to start with the sensor connected. When I disconnect it, the glows come on for 10 seconds, and the truck fires up better than new.

Would it be advisable to replace both sensors at the same time since I'll be draining some of the coolant anyway? I don't know how old the dash gauge sensor is so it might be on borrowed time as well perhaps. Any thoughts?

Also, are the two coolant temp sensors the same part number and identical internally?

Thanks for the help!

~Greg

[sixnickel]

The temp senders are different the ECM sender in the water manifold is a 2 wire and the guage sender is a 1 wire. You do not need to drain the cooling sys. to change the senders. Just have the new one ready to go with thread sealant take the old one out with one hand the new one in the other hand.out and in bang,bang. You will lose a little coolant but no big deal! The part # for SSDiesel Supply is SSD-053 for the guage sender. Also loosen the rad cap so there is no pressure in the system. Good Luck!

[greg2010]

Great! Thanks sixnickel for the info. I'll head out to my parts store this afternoon and see if I can locate the sender for a reasonable price (it's nice weather today and I'd like to get the job done and over with). If not, I'll order it from Walt and install it next weekend.

One final question for you SixNickel...What type of sealant should I use? I've got some black RTV sealant, but I don't think it's necessarely the appropriate sealant for this application. Any suggestions?

Thanks again,
~Greg.

[sixnickel]

Permatex makes a liquid teflon thread seal I use all the time part# 59235 its great stuff. You also it on head bolts and timing cover bolts on the 6.2/6.5. Teflon tape or pipe dope will work also. Good Luck and have fun

[greg2010]

thanks sixnickel. I'm off to the parts store now. I'll let you know how I made out. :)

[greg2010]

Alright, I got the cooling temp sensor problem fixed up, and now there's a code 26 tripping--"Accelerator Pedal Position 2 Circuit Low" Since this truck has the "drive by wire" setup, am I looking at replacing the accelerator pedal assembly? Is there any way to test for this? There are no driveability problems with the truck at all. I've never noticed random acceleration/deceleration and everything seems to work normally. Any thoughts??

[sixnickel]

My guess is the APP is on its way out. If its running ok now I'd run it and see what happens. It might start acting up tomorrow, or next year! The APP is a expensive Part if you don't need it right now. But as soon as it acts up replace it. I haven't had one of these fail on me on a 6.5 so I don't know how they feel when they go bad. I have had them go bad on the International T444Es( power joke) at work. Know how they feel and I imagine they feel the same. Good Luck!!

[Husker 6.5]

Alright, I got the cooling temp sensor problem fixed up, and now there's a code 26 tripping--"Accelerator Pedal Position 2 Circuit Low" Since this truck has the "drive by wire" setup, am I looking at replacing the accelerator pedal assembly? Is there any way to test for this? There are no driveability problems with the truck at all. I've never noticed random acceleration/deceleration and everything seems to work normally. Any thoughts??

In a nutshell, yes. You used to be able to get just the pedal position sensor as a seperate part from GM for about $50. The early 94's had two sensors, when one failed, the computer would read the resultant signal in such a way that it would put the engine into WOT until it blew! Production was halted until GM could come up with a solution. That's why there is a couple of month gap in the production code dates on the Vehicle Data Plates. GM redesigned the pedal assy with three sensors for redundancy, and reprogammed the computer to eliminate the WOT problem. Later model pedal assys are supposed to work with the early harness. Had to do it on my 94 C2500HD.

For more info, see the Throttle Either On or Off thread in the Engine forum, dtd 2-20-07.

Concerning your temp. gauge and ecm temp. senders. Word of advice from personal experience. Do not use discount automotive store senders, their accuracy is questionable at best. When I bought mine used and went to Houston to bring it back, I noticed that the temp gauge didn't work. I stopped in Wichita at an Auto Zone and bought a Wells sender and installed it. My gauge was reading in the red zone all the way back to Lincoln, and I was freaking over it. Went to my mechanic the next morning, his thermal scanner on the thermostat housing said I was running 182* when the gauge was pegged!! Went to the GM dealer and got a sender, it was $5 cheaper than the "discount", and dead on accurate, plus it came with thread sealant already on the threads. Walt's are OEM, and are cheaper than the Dealer.

Husker 6.5:D

[greg2010]

I've been using Wells products for a long time Husker on my gas jobs and my 6.5. I've had a couple things go bad, but for the most part they've held up over time. The temp sender only cost about $20 canadian, so if it goes bad, I'll get the one from Walt with my next order. The only reason I didn't order from walt this time is because the shipping and import tax would be more than the part itself.

The accelerator pedal assembly you're both speaking of, is it the one that is integral to the pedal in the cab or am I looking at something attached to the IP? I assume the one in the cab, but with all the electronics on this motor I can never be sure. :p

[sixnickel]

The APP is part# ssd-234 at SSD Supply it is the first item under sensors look at the picture. It is the complete pedal assembly.

[greg2010]

Thanks gentlemen. I'm going to drive it for now and hopeully it will last a while longer until surplus funds allow for the repair....or until i trade it in as a boat anchor, whichever comes first.

Thanks again for the wealth of information. :)