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I have a 97 freightliner classic with a 12.7 ddec III my…

I have a 97 freightliner...
I have a 97 freightliner classic with a 12.7 ddec III my temp gauge stays at 175 most of the time but it fluctuates quite often. By fluctuating I mean it goes all the way and back to normal very quickly. Or it might go all the way down and then back to normal again very quickly. Sometimes it goes all the way up and then all the way down and then goes back to normal. Can someone help me. I replaces the coolant temp sensor thinking tjat was the issue. No lights come on in my dash.
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Answered in 1 hour by:
3/9/2018
Daniel Wilson
Category: Medium and Heavy Trucks
Satisfied Customers: 6,792
Experience: Owner at DJ Wilson
Verified

Hi ,My name is Dan. I will be glad to help. We can follow up as needed on here, Give me some time to review your information and post my responses. Im not an employee of the site but I help on here as time allows in between jobs. Response time will vary depending on my work load , etc. Are there any fault codes logged in the ECM memory?

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Customer reply replied 4 months ago
I dont know how to pull the codes. I do not have a way to scan the ecm.

Is the check engine light on and staying on?

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If you replace the sensor already then the problem with the gauge fluctuating that way will either be a shaved or shorted Connection in the wiring harness causing a voltage Spike that will throw off the gauge signal or the problem is in the gauge itself. Try a wiggle test on the wiring harness going into the gauges and see if you can get it to act up by wiggling the wiring harness and maneuvering the wires around the connectors and connector pins. This will help isolate a potential wiring harness problem rather than a gauge issue. If this doesn't reveal a wiring problem what you will want to do is use a voltage meter and then test voltage at the plug going into the gauges and see if the voltage stays consistent or if you're actually getting spikes of voltage into the cluster there are varying. If not I would have to say that it's a problem with the gauge itself if the power and grounds are good and consistent to the gauge. Look for any corroded connector pins and damaged wiring in the wiring harness. Also on your wiggle test I would check at the engine harness as well and have somebody in the cab watching while you perform a wiggle test on the engine side of the harness up to the firewall connector as well as checking for a corroded pins or connections. Let me know the results and please remember to take a moment to write my answers as that is how the site credits my time helping on the site. Five-star ratings in bonuses are always greatly appreciated.
Daniel Wilson
Category: Medium and Heavy Trucks
Satisfied Customers: 6,792
Experience: Owner at DJ Wilson
Verified
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Customer reply replied 4 months ago
Hi. I will accept your answer now and will test and update you over the weekend.

Pleasure to help.

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Customer reply replied 3 months ago
Sorry I was not able to get back to you sooner. I tried the wiggle test when the engine was cold and nothing. I just noticed it seems to only do it after engine warms up. I will try again later today after the engine warms up.

Thanks for the update. Keep me posted.

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Customer reply replied 3 months ago
I have tried the wiggle test multiple times and cannot seem to find anything wrong. The computer is giving me Code 53. Could that be the problem? I know when I had a scanner hooked up it said 253 FMI 12 or something similar. Something about volotile memeory.
Thanks for the update. If you have good power and ground to the ECM that fault is for a failed ECM in need of replacement. It is possible to try reprogramming your existing ECM to see if you may be successful where they reprogram however be prepared that you maybe replacing the ECM.
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Customer reply replied 3 months ago
Ok. The guy I purchased the truck from a year go said that code has been there for the longest and he had the ecm reprogram once but the code Still came up so I guess I may as well replace it and hope that it also cures the malfunctioning temp gauge.
If the wiring harness and Gage are okay along with the sensor then the ECM is the only thing left and where it's already having some issues it will at least correct those. That would be great if it corrects your gauge issue as well.
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