Temperature needle pegging

[regalrobert]

The temp guage on my 2000 Regal is pegging intermittingly when I am driving and seems to happen more when I am stepping on the brake. I have replaced the temp sensor and the plug for the sensor. Any suggestions on where to look next.

[BNaylor]

Welcome to AF.

And you are sure the car is not overheating? Does the temp overheat indicator ever come on?

Sounds like you may have a problem like possible internal shorting in the Instrument Panel Cluster (IP). There are various diodes that route and isolate signals from sensors and switches to the respective gauge or idiot light.

Also, I hope you did not use plumbers tape on the ECT sensor.

[regalrobert]

Thanks for responding. The car is running perfectly. The only problem is when the temp indicator pegs for a few seconds it makes a sensor think the car is actually hot and starts shutting things down like the TRAC control. Once in a great while it cuts out when this happens, but very very seldom. Also, No plumbers tape used anywhere. Only proper devices. I used the crimp-type connectors provided with the temp sensor plug when I changed it out.

[regalrobert]

Could my problem be a loose connector under the dash or maybe a ground wire loose letting some electricity sink through other devices to my tempsensor?

[BNaylor]

It is possible. I would check the battery connections too. Make sure terminals are tight and free of corrosion especially the negative cable and at the alternator.

The connections on the back of the IP are hard to get to without removing the lower dash panels and the plastic dash bezel. Also, check the powertrain control module (PCM) 80 pin connectors. PCM is located in the air box. The PCM is the control device that monitors ECT temperature via the sensor and gives the signal to the temperature gauge. Try removing the battery negative cable for a few hours and then see what it does.

[regalrobert]

When you say the air box, what are you refering to? I will check all my grounds and remove the negative cable tonight.

[BNaylor]

Originally Posted by regalrobert

When you say the air box, what are you refering to? I will check all my grounds and remove the negative cable tonight.

The PCM module is enclosed inside the air filter assembly. You'll see the main wiring harness towards the bottom of the air box. To access the box must be disassembled to expose the PCM module. I would try the battery negative cable disconnect first. Also, if you have a multimeter check the output of the alternator for around 14.5 dc volts. The part that sounds weird is when you press the brakes which could mean the alternator is not putting out the proper voltage. Another suggestion is to check with GM or a dealer and see if your PCM has the latest software/firmware update. A PCM reflash may help if it is not an actual electrical problem.

[regalrobert]

Continuing to scratch my head. I took my Regal to AAMCO and had the full diagnostic run. Good news/bad news. Nothing showed up as being really wrong. The right rear wheel sensor was giving an error, but I have had a slow leak in that tire, which could cause the error due to change in rotation from the tire pressure. But, the temp guage is still pegging intermittently, so I am going gremlin hunting wire by wire. I still need to check voltage at the alternator. Any additional suggestions are certainly welcome.

[BNaylor]

Just as simple test which may not prove anything with the engine off disconnect the electrical connector from the engine coolant temp sensor (ECT). Turn ignition switch to ON and see what the temp gauge does. It should read to the far left at the C mark. Then start engine and see what the indication is. If the gauge still pegs or even reads anything then I would say it is most likely an IP Cluster related problem.

[regalrobert]

Thanks. I'll give it a try. I have started opening up the wiring bundles and tracing the temp sensor wires to see if there are any breaks in the insulation. I'm determined to get to the end of this puzzle.

I saw on your profile that you are a BSEE from El Paso. Were you an NMSU BSEE? I graduated from there in 1984. Started in EE but changed to Business after co-oping with a company in Lubbock.

[BNaylor]

Hopefully you find the problem outside of the IP. The IP is expensive through the dealer. You can get a good price at a salvage yard or on EBay but the problem is the odometer module is located in it so it would need to be programmed with your current mileage. I only know of one company that does that type work to include IP repair. Southern Electronics.

NMSU is Las Cruces? You're an Aggie. I'm a Texas Tech Red Raider. I have a few friends that graduated from NMSU and work for Lockheed in Las Cruces and at White Sand Missile Range. Nice chatting. Good luck.

[regalrobert]

I finally had time to get back to working on this. I unplugged the Temp Sensor leads to see if it did anything. The guage still registered and still jumped around. Also, when the sensor was unplugged it ran rough and clattered like when you have octane issues.

I am going to start tracing wires individually to see if I can find a short.

[regalrobert]

I finally got the problem sovled!!!!!!!!! After changing the temperature sensor, the plug to the sensor, having diagnostics run, checking the alternator, and the battery, I found the culprit. I began tracing individual wires. I started at the temperature sensor itself and traced the wires to the unit underneath the air intake box. The plastic flex tubing over the wires was gapped at a bend, and there was a rubbed spot on the wire at that bend. When I got to the wire, it had a place where the insulation was off, and had been contacting metal on the frame near the air intake box. I repaired the nick in the wire, checked all other wires near it, none of which were damaged, then covered and taped the wire bundle. I have not had a single dash light malfunction since. WOOOO HOOOO!!

[Luke.]

Congratulations, and as important, thank you for the follow-up report.