95 Yukon - Weird Coolant Temp Sensor (to ECM) Issue

[italie]

Hi all,

I recently blew a TBI gasket, so I decided to bite the bullet and clear out my trucks "to-do" list.

Pre-work:
I had codes 22,32,35,54 stored in the computer before the work, and the MIL would come on every so often while driving and turn off after a minute or two. I've owned the truck since '08, and have put roughly 70K on it. (At 264K now)

Work Done:
I replaced the TBI mount gasket. I cleaned out/degunked the TBI assembly. I replaced all the gunked up vacuum lines between the TBI and EGR, PCV, etc. I replaced the EGR valve and the PCV. EGR solinoid is 2 years old. IAC is a year old. I cleaned the IAC, but it wasn't that dirty. Replaced the ripped air inlet pipe, as well as the air filter. (eventually replaced both the coolant temp sensor to the ECM, and the pigtail)

The issue:
Overall the truck runs better than it ever has, except for the transition between idle and light acceleration, where it bogs severely. It did not do this before the work. The truck will run OK when it gets to speed, or at idle. I also now have a solid on MIL with codes 14 & 15 (Coolant Sensor Circuit Shorted & Coolant Sensor Circuit Open).
After replacing the sensor (TS4052 from Napa), I checked it for proper operation. I measured it from 800 Ohms down to 200 ohms while the engine heated. Same issue of bogging on light acceleration, MIL on.

5V is present on the pigtail, ground appears solid. I replaced the pigtail just to be sure, same issues.

The strangest part is that if I put a 470 ohm resistor across the pigtail, the truck runs fine and the MIL turns off. Slightly rough at times, but overall no hesitations or bogging on a 7 minute trip to the auto parts store. Could I have bought a bunk sensor? ECM toast? Other thoughts?

I can live with keeping the resistor in place for the short term, but I am absolutely out of ideas on the sensor short of buying another one...even though this one appears OK on the multi meter.

Appreciate any advice you can give.



'95 GMC Yukon 5.7L 4WD 2DR

 

[SunlitComet]

the 470 resister makes the ecm think the engine is at about 160° which is to low. you are burning a rich mixture at that point and will do damage later on. when hot from driving around the sensor should read about 177 ohms at 212°. 200 ohms would put you at 130°. with any sensors on your suv delphi or acdelco parts are pretty much a necessity here. and your code description is off. 14 means the computer sees the engine above 270° and 15 means you are below 31°. i suggest you recheck your pigtail install and put a Delphi sensor in there. and then we can go from there.

 

[italie]

the 470 resister makes the ecm think the engine is at about 160° which is to low. you are burning a rich mixture at that point and will do damage later on. when hot from driving around the sensor should read about 177 ohms at 212°. 200 ohms would put you at 130°. with any sensors on your suv delphi or acdelco parts are pretty much a necessity here. and your code description is off. 14 means the computer sees the engine above 270° and 15 means you are below 31°. i suggest you recheck your pigtail install and put a Delphi sensor in there. and then we can go from there.

We are essentially saying the same thing about the codes, I was just using the generic GM OBD1 terms.

I choose 470 as a resistor value as a nice "midpoint" to get me back tot he autoparts store, I don't think the truck wouldn't have made it with the temp sensor connected, and it won't start without it connected.

Pigtail meters fine, and the leads were connected with solder and heat shrink.

I'll pickup a delphi sensor tomorrow and give it a try.

 

[SunlitComet]

disconnect the battery when you pull out the old and reconnect when new one is in so the codes clear out and see what comes back.

 

[italie]

disconnect the battery when you pull out the old and reconnect when new one is in so the codes clear out and see what comes back.

I've been doing that in between old/new sensor swap and even when the resistor is put in place. No codes with resistor in place, 14 & 15 thrown immediately with the new sensor.

The connector housing snapped off the old sensor taking it out, so I haven't re-checked with it installed.

 

[italie]

Brief update. I swapped the temp sensor for a Delco with no improvement. Still throws codes 14&15, but also threw a 22 the last time I drove it. Put a TPS in it, and no codes have been throw so far. No sign of the MIL yet either.

 

[SunlitComet]

if wires is intact and with no faults them something is wrong with the ecm them. each sensor has it own ground to ecm so if there are no damaged grounds from ecm to body to batt and connectors to ecm are secure and clean and all other wiring is good fault lies with the ecm.

 

[italie]

if wires is intact and with no faults them something is wrong with the ecm them. each sensor has it own ground to ecm so if there are no damaged grounds from ecm to body to batt and connectors to ecm are secure and clean and all other wiring is good fault lies with the ecm.

TPS appears to have solved the issue, no MIL since replacing it. There must be some link between the CTS and the TPS in the ECMs embedded code.

 

[SunlitComet]

actually there is not but i will look into the resolution you did tho. let me know if something changes.

 

[italie]

actually there is not but i will look into the resolution you did tho. let me know if something changes.

After a week of heavy driving, no change. No MIL, no codes thrown. Truck is running great. (Knock on wood)