Mechanics

F150 COOLANT GAUGE NOT WORKING

1998 Ford F-150

Electrical problem
1998 Ford F150 V8 Two Wheel Drive Automatic 171000 miles

Coolant Temp Guage on my 98 f150 2wd 4.6 auto is not working. Checked the sensor, replaced with new one and still nothing. Then checked ohms at sensor and was ok, did not show open circuit.

What volts should I see when checking the opposite end of pigtail that plugs into sensor?

What should I check next?

Getting heat in cabin but truck seems to have a rough idle. Dont think computer is getting correct engine temps.

ecm sensor 25000 ohms and going down as I take measurements. Gauge sensor 2700 ohm and going down as well. Seems like as I hold sensor in hand ohm go down but if I stand sensor upright ohm stay steady? 25k ohms seems kinds high. What do u think?

Will place sensors in pot of hot water and post findings.

Thanks.
Avatar
Robjs111
November 29, 2009.




1. Disconnect Sensor - Ensure temperature sensor connector is in good condition. Turn ignition off. Disconnect coolant temperature sensor. Turn ignition off. If temperature gauge indicates does not indicate cold, go to next step. If temperature gauge indicates cold, go to step 3). 2. Check Red/White Wire For Short To Ground - Turn ignition off. Measure resistance of Red/White wire between coolant temperature sender connector and ground. If resistance is more than 10 k/ohms, go to step 4). If resistance is less than 10 k/ohms, repair Red/White wire. Retest system. 3. By-Pass Temperature Sensor - Connect a jumper wire between the 2 pins of temperature sensor harness connector. If temperature gauge indicates hot, replace coolant temperature sensor. If temperature gauge does not indicate hot, go to step 5). 4. Check Red/White Wire For Short To Ground - Turn ignition off. Disconnect instrument cluster harness connector C237. Measure resistance between instrument cluster harness connector C237 pin No. 9 (Red/White wire) and ground. If resistance is more than 10k/ohms, repair/replace instrument cluster. If resistance is less than 10 k/ohms, repair short to ground in Red/White wire. Check gauge operation. 5. Check Red/White Wire & Pink/Orange Wire For Open - Turn ignition off. Disconnect instrument cluster harness connector C237. Measure resistance between C237 pin No. 9 (Red/White wire) and pin No. 5 (Pink/Orange wire). If resistance is less than 5 ohms, repair/replace instrument cluster. If resistance is greater than 5 ohms, repair open Red/White or Pink/Orange wire. Retest system.
Test ECT this way.


http://www.2carpros.com/forum/automotive_pictures/62217_ect_5.jpg

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Merlin2021
Nov 29, 2009.
There are 2 sensors one black and the other gray. The gray sensor is inboard to the black sensor and both located top pass side intake manifold. Also both sensors on same wiring harness. Sensors look fine, no leaks or corrosion. Checked each sensor with engine on: black 13.3 v / 670 ohms
gray 4.6 v / 1540 ohms

engine off: both showing 800 ohms, about.

Installed jumper between the sensor connectors and still gauge showing hot.

Can you tell me what each sensor is, function of?

Also with connectors off and engine on temp gauge still pegged at Hot.

Do I have a short?

Also both have red/white wires. One with red and white stripes the other is white with red stripes.
Edit/Delete Message

Tiny
Robjs111
Nov 29, 2009.
Temp gauge sender has red/white stripe and yellow/red stripe, yellow/red is the ground red/white is gauge wire. ECT has lt green/red stripe and gray/red stripe.


http://www.2carpros.com/forum/automotive_pictures/62217_sender_1.jpg



http://www.2carpros.com/forum/automotive_pictures/62217_ECT_11.jpg


Check red/white for short to ground.

Merlin2021
Nov 30, 2009.

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