az4x4tahoe
TYF Newbie
- Joined
- Feb 7, 2022
- Posts
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Hello everyone, I'm new here. I recently went through some challenging troubleshooting on my Tahoe, and I figured I'd write it up in case anyone has the same problem in the future.
To start off, I have a 2006 Tahoe LS. It's a 4wd and it has about 209k miles.
My electric cooling fans were staying on after I'd remove the key. I first found this out when I had a dead battery one morning. After getting the battery charged, as soon as I hooked it back up, the cooling fans immediately turned on. I did some investigating to figure out what the problem might be.
The cooling fans are controlled by the PCM. It evaluates the data it gets from the Engine Coolant Temperature (ECT) sensor and decide when it should be turning on the fans. It can turn the fans onto a high speed or a low speed. This is all accomplished via a wire harness and three relays. Note, the relays are not located under the main fuse box. There are under a separate fuse box right next to the main fuse box.
I was able to verify that my ECT was getting 5V on one pin and zero volts on the other. I checked the relays, and they were all fine. This meant that the problem was either in the wiring harness, or I had a bad PCM. I pulled the PCM and looked at the pins. Sure enough, I could see some corrosion on pin 42. When pin 42 is shorted to ground, this is how the PCM turns the fans onto low speed. I cleaned off the PCM pins as best I could and put it all back together. This fixed the problem for about a day.
After the problem came back, I recognized that troubleshooting a wire harness problem was outside my capabilities. So I took the Tahoe into the repair shop. They were able to find that the connector that mates to the PCM had corroded receptacles. They ended up having to replace a few of the receptacles in the wire harness. After that, the Tahoe ran fine... until three days later.
To make this next part shorter... It turns out that when I used my DMM to test the ECT connector, I had damaged the receptacle springs. This was causing the ECT sensor to provide intermittent readings to the PCM, which resulted in the wrong air fuel mixtures being commanded. I replaced the ECT sensor connector (this is actually pretty easy to do), and the problem was resolved.
If you do happen to have this problem. Here are the problems that could be your root cause.
1) Bad ECT sensor
2) Failed relays - there are three of them
3) Wiring harness problem
4) PCM problem
I spent almost three weeks fighting through this in one way or another. I hope this write up can help someone get through their problem faster than I got through mine.
To start off, I have a 2006 Tahoe LS. It's a 4wd and it has about 209k miles.
My electric cooling fans were staying on after I'd remove the key. I first found this out when I had a dead battery one morning. After getting the battery charged, as soon as I hooked it back up, the cooling fans immediately turned on. I did some investigating to figure out what the problem might be.
The cooling fans are controlled by the PCM. It evaluates the data it gets from the Engine Coolant Temperature (ECT) sensor and decide when it should be turning on the fans. It can turn the fans onto a high speed or a low speed. This is all accomplished via a wire harness and three relays. Note, the relays are not located under the main fuse box. There are under a separate fuse box right next to the main fuse box.
I was able to verify that my ECT was getting 5V on one pin and zero volts on the other. I checked the relays, and they were all fine. This meant that the problem was either in the wiring harness, or I had a bad PCM. I pulled the PCM and looked at the pins. Sure enough, I could see some corrosion on pin 42. When pin 42 is shorted to ground, this is how the PCM turns the fans onto low speed. I cleaned off the PCM pins as best I could and put it all back together. This fixed the problem for about a day.
After the problem came back, I recognized that troubleshooting a wire harness problem was outside my capabilities. So I took the Tahoe into the repair shop. They were able to find that the connector that mates to the PCM had corroded receptacles. They ended up having to replace a few of the receptacles in the wire harness. After that, the Tahoe ran fine... until three days later.
To make this next part shorter... It turns out that when I used my DMM to test the ECT connector, I had damaged the receptacle springs. This was causing the ECT sensor to provide intermittent readings to the PCM, which resulted in the wrong air fuel mixtures being commanded. I replaced the ECT sensor connector (this is actually pretty easy to do), and the problem was resolved.
If you do happen to have this problem. Here are the problems that could be your root cause.
1) Bad ECT sensor
2) Failed relays - there are three of them
3) Wiring harness problem
4) PCM problem
I spent almost three weeks fighting through this in one way or another. I hope this write up can help someone get through their problem faster than I got through mine.
