Hi garym, There are two temperature sensors, a single-wire sensor for the temperature gauge, and a two-wire sensor for the engine computer. That's the one monitored by the engine computer.
There are two possibilities. You can measure the voltage on the sensor but it must be plugged in. The ground wire should have around 0.2 volts. The signal wire must have between.5 and 4.5 volts depending on coolant temperature. A voltage outside that range is what tells the engine computer to record the diagnostic fault code. The code is not meant to indicate the specific part that is defective, just the circuit with the problem.
If you find near 0 volts on the signal wire, the wire is likely grounded somewhere. It is not open, (broken) because that would send the voltage high, to 5.0 volts at the computer. That would set a different code.
If you find the signal voltage is between.5 and 4.5 volts, (lower voltage equals higher temperature), but it continues to set a code, you'll need to read the sensor voltages with a hand-held computer commonly called a scanner. Look at the ambient air / battery temperature sensor in particular. No two sensors are exactly alike. The engine computer compares a lot of stuff to learn the characteristics of various sensors. As an example, the computer knows that after the engine has been off for a specific period of time, the coolant temperature sensor and the battery temperature sensor should be at the same temperature. If they disagree substantially, you'll have to determine with the scanner which one is incorrect.
Be sure too that the codes really got erased. Disconnecting the battery was a common way to do that but it also erased all the stored fuel trim data from the engine computer's memory. 2004 is when they started phasing in the new CAN buss system which I'm not real familiar with. It could be possible the codes can only be erased with the scanner. If the scanner says the codes are eased, the next clue to look for is when they come back, if they do. If they are recorded right after starting the engine, a wiring problem is likely. If the codes don't set until well after the engine starts to warm up, suspect a sensor problem more so than an intermittent wiring problem.
Automatic Idle Speed motors don't really cause a lot of trouble. I'd suspect a wiring problem first, such as a loose or corroded pin in an electrical connector. The Chrysler scanner can run idle speed up and down to test the computer's ability to control the motor. An easy way to verify it is working is to look for the idle flare-up at engine startup. When started, the engine should immediately go to around 1500 rpm, then down to around 800 rpm after a couple of seconds. Another symptom of a non-responsive AIS motor is engine stalling when coming to a stop.
Tuesday, February 23rd, 2010 AT 7:09 AM