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Old 09-12-2018
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Default Temp Gauge issue

Hey guys,

I have an 05 TJ

I popped my OE radiator last week and I have replaced it with a new one.

On cold startup the needle on my temp gauge goes straight to half way and sits there. Cools a touch after 10 minutes or so.

Just wondering is anyone has any ideas on what to do to rectify this or if it is normal.

Last edited by JKnoob; 09-12-2018 at 04:11 PM.
  #2  
Old 09-12-2018
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Not normal. Maybe the sensor, connector or wiring have a problem.

Try the actuator test first to make sure the cluster function is normal. Press and hold the odometer reset button, turn the ignition on then release the button. The cluster will run the actuator test and all of the small needles should move in the same manner.
If that's OK have a look at the temperature sensor and wiring in case any of it was disturbed/damaged during the radiator swap.

Assuming the temp sensor is the same as in earlier models the chart below can be used to compare the sensor resistance and see if it is in spec.




Here's what the 05 FSM states about the gauge operation...

ENGINE TEMPERATURE GAUGE

DESCRIPTION

An engine coolant temperature gauge is standard equipment on all instrument clusters. The engine coolant temperature gauge is located in the lower right quadrant of the instrument cluster, below the oil pressure gauge. The engine coolant temperature gauge consists of a movable gauge needle or pointer controlled by the instrument cluster circuitry and a fixed 90 degree scale on the cluster overlay that
reads left-to-right from 40° C (or 100° F) to 125° C (or 260° F). An International Control and Display Symbol icon for “Engine Coolant Temperature” is located on the cluster overlay, directly above the hub of the gauge needle. The engine coolant temperature gauge graphics are white and blue against a black field except for a single red graduation at the high end of the gauge scale, making them clearly visible within the instrument cluster in daylight. When illuminated from behind by the panel lamps dimmer controlled cluster illumination lighting with the exterior lamps turned On, the white graphics appear white, the blue graphics appear blue, and the red
graphics appear red. The orange gauge needle is internally illuminated. Gauge illumination is provided by replaceable incandescent bulb and bulb holder units located on the instrument cluster electronic circuit board. The engine coolant temperature gauge is serviced as a unit with the instrument cluster.

OPERATION

The engine coolant temperature gauge gives an indication to the vehicle operator of the engine coolant temperature. This gauge is controlled by the instrument cluster circuit board based upon cluster programming and electronic messages received by
the cluster from the Powertrain Control Module (PCM) over the Programmable Communications Interface (PCI) data bus. The engine coolant temperature gauge is an air core magnetic unit that receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the On or Start positions. The cluster is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the Off position. The instrument cluster circuitry
controls the gauge needle position and provides the following features:
† Engine Temperature Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is between about 40° C (100° F) and 124° C (255° F), the gauge needle is moved to the actual relative temperature position on the gauge scale.

† Engine Temperature Low Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is at or below about 40° C (100° F), the gauge needle is held at the 40° C (100° F) graduation at the far left end of
the gauge scale. The gauge needle remains at the left end of the gauge scale until the cluster receives a message from the PCM indicating that the engine temperature is above about 40° C (100° F), or until the ignition switch is turned to the Off position, whichever occurs first.

† Engine Temperature High Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is above about 127° C (261° F), the gauge needle is moved into the red zone at the far right end of the gauge scale, the check gauges indicator is illuminated, and a single chime tone is sounded. The gauge needle remains in the red zone and the check gauges indicator remains illuminated until the cluster receives a message from the PCM indicating that the engine temperature is below about 124° C (255° F), or until the ignition switch is turned to the Off position, whichever occurs first. The chime tone feature will
occur only once per ignition cycle.

† Engine Temperature Critical Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is above about 129° C (264° F), the gauge needle is moved to the far right end of the red zone on the gauge scale. The gauge needle remains at the far right end of the red zone until the cluster receives a message from the PCM indicating that the engine temperature is below about 127° C (261° F), or until the ignition switch is turned to the Off position, whichever occurs first.

† Communication Error - If the cluster fails to receive an engine temperature message, it will hold the gauge needle at the last indication about twelve seconds or until the ignition switch is turned to the Off position, whichever occurs first. After twelve seconds, the cluster will move the gauge needle to the left end of the gauge scale.

† Actuator Test - Each time the cluster is put through the actuator test, the gauge needle will be swept to several calibration points on the gauge scale in a prescribed sequence to confirm the functionality of the gauge and the cluster control circuitry. The PCM continually monitors the engine coolant temperature sensor to determine the engine operating temperature. The PCM then sends the proper engine coolant temperature messages to the instrument cluster.

If the instrument cluster turns on the check gauges indicator due to a high or critical engine temperature gauge reading, it may indicate that the engine or the engine cooling system requires service. For proper diagnosis of the engine coolant temperature sensor, the PCM, the PCI data bus, or the electronic message inputs to the instrument cluster that control the engine coolant temperature gauge, a DRBIII scan tool is required. Refer to the appropriate diagnostic information.
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Old 10-12-2018
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Thanks mate. lots to go through, but I've got a start point no so its much appreciated.
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Old 10-12-2018
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What a great write up from JJ, some useful info in there for me to try on my 04 TJ, always wondered what the actual temperature is compared with the needle position.

I was thinking about your problem and trying to understand what kind of electrical issue would give those symptoms (assuming nothing else has changed) and couldn't really come up with a good theory. To go straight to 100 with key on, youd need a low resistance between the connected module and ground. If the sensor was still connected in parallel but functioning the gauge would be higher than the expected value. The two resistances in parallel would create a slightly lower resistance, so a slightly higher temperature. Then when the actual sensor heated up as its resistance fell, the gauge would eventually start to read too high - but you said it reduces a fraction after warm up.

Its hard to imagine what could happen to the sensor during a flush, but who knows.

Id start by disconnecting the sensor, leave the wire hanging and start the engine. In my TJ this brings the engine management warning lamp on, because it detected a failed sensor and it's an emissions fail. Don't panic after the 4th engine start with it reconnected the fault self heals.

In your case if there is a damaged wire but your module still sees a resistance which equates to 100c approximately, the gauge will read ok, the warning lamp wont come on and you will have to focus on the wiring.

On the other hand, if you get an engine warning lamp (stays on when running) and your gauge is stuck cold then id have to assume for some reason a sensor, or less likely, grounding problem. If you wanted to get a bit more scientific in this scenario, pop into Jaycar and buy a 1.2Kohm resistor, hang it on the end of the connector between the two pins gently. And expect to see about 80c on the gauge, proving your diagnosis of the sensor before you buy one.

But overall, ask yourself what you might have physically disturbed, bumped, crunched or pulled during the other work.

A bit generic, but interested to know what you eventually come up with.
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