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Stock JK TechBulletin board forum regarding issues with OE (original equipment) components of the Jeep JK Wrangler (Rubicon, Sahara, Unlimited and X) such as factory suspension parts, engine, transmission, body parts, interior fixtures and the on-board computer.
Just got my 08 Wrangler 2 door and have been loving it. One issue I have run into that I cannot figure out is that every few days upon the initial start of the vehicle I will be driving a few miles and then the temperature gauge will suddenly drop to zero and will not read at all. If I turn off the jeep and restart it, it will read accurately again and I will not have the problem for the rest of the day. I have replaced the thermostat and the coolant temperature sensor with no change. I have made sure all battery connections are tight. It is driving me nuts and if I don't catch it quick enough it will throw the CEL (cooling system implausible temperature reading--autozone suggested thermostat replacement). Has anyone had the same problem or know what I could do to troubleshoot this??? Thanks!
Theory of Operation
The PCM predicts what the engine coolant temperature should be, based on the engine coolant temperature at start-up, ambient temperature and how the vehicle is subsequently driven. The predicted engine coolant temperature is compared to the Engine Coolant Temperature Sensor reading. The error between the two is calculated and integrated with respect to time. When the Thermostat diagnostic runs, the integrated error is compared to a calibrated threshold and pass/fail is determined. Separate pass and fail thresholds are used in order to improve accuracy of the diagnostic.
When Monitored: Engine running.
Set Condition: This diagnostic will fail when the model temperature reaches 91 degrees C (196 degrees F) before the ECT. reaches 80 degrees C (176 degrees F. This monitor only runs after a cold start condition ECT, ACT, AMB are all within 10 degrees C (50 degrees F. of one another. Two Trip Fault. Three good trips to turn off the MIL.
Possible Causes
LOW COOLANT LEVEL
THERMOSTAT OPERATION
SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE
TEMPERATURE SENSOR
SIGNAL CIRCUIT OPEN
SENSOR GROUND CIRCUIT OPEN
SIGNAL CIRCUIT SHORTED TO GROUND
SIGNAL CIRCUIT SHORTED TO THE (K900), (G931) SENSOR GROUND CIRCUIT
OTHER POSSIBLE CAUSES
PCM
So what do you suggest going forward? I’ve ruled out the coolant level, sensor and thermostat. Should I just take it to a mechanic for better diagnosis? A dealership?
Below is the schematic. The wire colors, pins, connectors, are all on the scheme. What to do, and whether to take it to a tech depends on your skill level.
Since the temperature gauge falls to zero intermittently and you have already replaced the sensor, it's probably a bad connection or wire damage. The typically method is to take voltage/resistance measurements using the schematic in a logical fashion. But the problem may not show up at the time since it is an intermittent problem -- By definition, troubleshooting an intermittent problem is difficult. Wiggling wires, especially at a connector, during a resistance check is one way to find intermittent connections or broken/corroded stands of copper within wiring.
I'd start with a visual inspection, heat or rodent damage are possibilities that come to mind. The next easiest and most likely suspects are the connectors, maybe a corroded bad connection with male or female pin. Sometimes just breaking and making the connection a few times will work, sometimes electrical cleaner works (but make sure it's fully dry before assembly). I've also used NoOX electrical grease or petroleum jelly sparingly on pins to prevent further corrosion with good success.
The connector at the sensor itself has already been apart, but check it first since it's the easiest. Next connector per the schematic is C102, which is a large 20 pin connector (see the location diagram below). The last connector is C2 at the PCM itself. Remember to always disconnect battery neg unless power is necessary for the troubleshooting itself -- Do no harm.
Happy holidays! Stay in touch, curios what it turn out to be.
Last edited by Mr.T; 12-25-2018 at 12:46 PM.
Reason: spell check
Hello Joshpierce05,
Did you ever find out what was causing your gauge to drop to "C"; Im having the same issue. I have replaced the temp sensor and also the thermostat and I am still having the same issue. Curious to know if you ever sorted this issue out. Thanks in advance for your help!
BTW I have a 2010 JKU 3.8L.
Hello guys, I am having the same problem with my 2010 2DR, I have replaced the thermostat and temp sensor. Anyone ever get this one figured out? I am also getting ready to change the fan relay due to mine only running at high speed.
Hello guys, I am having the same problem with my 2010 2DR, I have replaced the thermostat and temp sensor. Anyone ever get this one figured out? I am also getting ready to change the fan relay due to mine only running at high speed.
Same problem I think. 2008 got the temp sensor code. Have replaced sensor 4 times last one was with a mopar sensor. Have replaced thermostat 3 times and now have replaced the harness side plug at sensor. Mine however is not intermittent
12-24-2018, 02:01 PM
Temperature gauge issue after inital start
