2nd Gen Non-Engine/Transmission MiniComputer Temp failure

[J D Moore]

I have a 99 CTD with the overhead minicomputer. Recently needed to re-set the compass and subsequently the temperature readout is wildly inaccurate usually in the + 200-350 range. I suspect the compass change is unrelated to the temp. problem, but the timing is peculiar.

I did a search and found a threat that included the following paraphrased remarks.



"I would take it to the dealer and have them look at it. It might be a simple fix - like a thermocouple"



"This is part of the manual description:

AMBIENT TEMPERATURE SENSOR

The temperature function is supported by the ambient temperature sensor, a wiring circuit, and Front Control Module (FCM). If any portion of the ambient temperature sensor circuit fails or if Programmable Communications Interface (PCI) Data Bus information is missing, a (- - ) will appear in the display in place of the temperature. When the sensor is exposed to temperatures above 55 C (130 F), or if the sensor circuit is shorted, 55 C (130 F) will appear in the display in place of the temperature, when the sensor is exposed to temperatures below - 40 C (- 40 F) or if the sensor circuit is open, - 40 C (- 40 F) will appear in the display. "



I suspect the sensor/thermocouple. Anybody know the location or have other information regarding the problem?



TIA

Jim

 

[tp0d]

I wouldnt doubt you have either a wiring short somewhere or a bad thermistor. The thermistor is usually located on the absolute front of the truck, on the grill itself or around the rad somewhere (facing forward). It should be a two wire connection hooked up to a small black box, possibly a round one. Reason I say its shorted is the computer is seeing full +5v return voltage, which will give you the max temp scale. If you unplug it, the reading may or may not change, but I believe the computer will say 'open' or 'nc' or something of the sort when its unplugged. (assuming the wiring is in good working condition). It isnt typical for the thermistor to short.



I did a quick search on rockauto.com for your part, and its pretty cheap (13-17$), if the sensor is bad that is... part numbers are : Standard#TX49 , Airtex#5S1136 , or ACDelco# 2133228



Good luck



-j

 

[damar]

I have a '98 24v and the temp reader box is on the front inside of the hood on my truck. Had to replace it once in 147,000 miles. Fixed the inaccurate temp problems.

 

[J D Moore]

tp0d & damar

Thanks for the excellent information. Sensor located behind hood grill on driver side of middle. RockAuto.com picture of Standard#TX49 & Airtex#5S1136 appear identical to my unit.

TDR is wonderful and people like you are what make it so.

Thanks again.

Jim

 

[J D Moore]

Follow up

I disconnected the sensor on Sunday to confirm which part to order. When disconnected the MiniComputer readout was OC (open circuit?). I then reinstalled it. Today the ambient temperature appears to be working, I suspect that a "software" reset occurred during the removal.

Thanks again.

Jim