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P0117 Coolant sensor low voltage CEL

A

alaskan

NAXJA Forum User
Location
Austin, TX
I'm getting this code on my 1997 4.0/AW4 Cherokee. The coolant temp gauge works fine so the first thing I did was have the Autozone guy clear the code. It came back a couple of days later and then gauge started going all over the place so I replaced the sensor. It was fine for a few days and then the CEL came back on.

In an unrelated incident, the radiator started leaking so I replaced it along with the coolant and a few hoses. Thinking I got a faulty part (a borg warner) I took it back and swapped in a second new sensor. It was fine for two more trips and then the CEL returned.

What could be causing this other than a bad sensor? The coolant no longer leaks and is full.
 
Since it is probably not the sensor, that leaves the sensor connector and the wire harness to be inspected or replaced.
 
As Tim mentioned, the "circuit" includes the sensor, connector, and all associated wiring.

I'd start by flushing the connector for the CTS with electrical contact cleaner, carefully inspecting the contacts inside the connector, apply a dab of dielectric grease and reconnect. Carefully inspect all wiring.
 
What's your alternator output? Check it with a multimeter, not your dash, at idle and revved up. I occasionally get a low voltage cel when doing a lot of low speed trail driving, although I think it's on the TPS circuit. I'm guessing that it's due to extended driving at basically idle speed. I have a ScanGauge, so I clear the code on the fly, and it I'm good to go.

Steve
 
birchlakeXJ said:
As Tim mentioned, the "circuit" includes the sensor, connector, and all associated wiring.

I'd start by flushing the connector for the CTS with electrical contact cleaner, carefully inspecting the contacts inside the connector, apply a dab of dielectric grease and reconnect. Carefully inspect all wiring.
Click to expand...

I cleaned it and reinstalled with dialectric grease while installing the second sensor. The contacts look fresh and the wiring doesn't look bad.

SteveT said:
What's your alternator output? Check it with a multimeter, not your dash, at idle and revved up. I occasionally get a low voltage cel when doing a lot of low speed trail driving, although I think it's on the TPS circuit. I'm guessing that it's due to extended driving at basically idle speed. I have a ScanGauge, so I clear the code on the fly, and it I'm good to go.

Steve
Click to expand...

I'll check that tonight, it usually reads just under 14 on the dash. I have been idling way more than usual (10 minute stretches) because of some roadway construction on my drive to work.
 
If the PCM sees the coolant temp signal drops below .8 volts for more than 3 seconds.

You ruled out the sensor but I'd suspect it's the wiring. The way I would test it is to unplug the PCM connectors and hook an ohm meter to the 18ga Tn/Blk wire in PCM connector C1 (black connector pin C16) and then move the harness around till you see the circuit short to ground. I'd bet it's at the back of the engine rubbing on the fuel rail.
 
MJR said:
If the PCM sees the coolant temp signal drops below .8 volts for more than 3 seconds.

You ruled out the sensor but I'd suspect it's the wiring. The way I would test it is to unplug the PCM connectors and hook an ohm meter to the 18ga Tn/Blk wire in PCM connector C1 (black connector pin C16) and then move the harness around till you see the circuit short to ground. I'd bet it's at the back of the engine rubbing on the fuel rail.
Click to expand...

I'll take a look at that tonight. So that wiring just runs up the fuel rail, across the firewall and down the fender to the PCM?
 
alaskan said:
I'll take a look at that tonight. So that wiring just runs up the fuel rail, across the firewall and down the fender to the PCM?
Click to expand...

Yes. I have seen one where the harness rubbed through at the back of the fuel rail. Just do a complete visual inspection of the wiring harness and look for places it might rub through and short to ground. A quick inspection may lead you to the problem. The only other cause (not sensor/wiring) would be the PCM itself.
 
I think I found the problem. I started working up the wire last night and found that the ground strap stud near the back of the head had worn into the harness and was rubbing against one of the wires to the temp sensor. I didn't have time to cut further up and replace the wire last night so I just taped the wire and then taped around the harness. I'm going to have Autozone clear the code at lunch and we'll see if it comes back this time.

Good call by MJR, he pretty much nailed this one.
 
alaskan said:
I think I found the problem. I started working up the wire last night and found that the ground strap stud near the back of the head had worn into the harness and was rubbing against one of the wires to the temp sensor. I didn't have time to cut further up and replace the wire last night so I just taped the wire and then taped around the harness. I'm going to have Autozone clear the code at lunch and we'll see if it comes back this time.

Good call by MJR, he pretty much nailed this one.
Click to expand...

Looks like the CEL is staying off after having it cleared.
 
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