p0112 and p0117 - Diagnosis Help?

Hi Folks! New to , new to XJs in general, but not totally new to cars and wrenching.

Just bought my first XJ -

1999 Cherokee Classic, 4.0L, Auto.

I've started getting these errors together:

P0112 - Low Intake Air Input
P0117 - Low Engine Coolant Input

I've pulled the sensors, both spec in range for resistance, and when I probe the connector, I appear to have 5V across the pins. Also, the temp gauge will intermittently zoom up to 260+, then come right back to the bottom - sometimes in the first 5 minutes of turning the engine on.

This screams an intermittent issue - maybe grounding? As I'm new to these, is there an obvious place to start? Frustrated from a night wrenching on it, but next steps that I can think of are pulling ECU connectors and cleaning, and working my way out.

Anything that would help narrow down the search appreciated. Thanks all!

The image below illustrates the results of me testing my ECT and IAT wiring at their connectors. I had/have no problems, I was just curious.

The tests were conducted with the connectors installed and back probed. Temps around 70*F.

If you remove the connectors and probe the pin cavities with the Brown/Yellow tracer wires going to them you should read .015-.020 volts with ignition switch to ON/RUN. If the voltage is 5 volts there is a short to the 5 volt supply to other sensors.

If the ECT/IAC voltage is out of spec, remove the connector from the TPS and read the voltage at the Brown/Yellow tracer pin cav. See if it's in spec.

If you are seeing voltage problems wiggle the wire looms and see if there are any changes. Occasionally the wire loom at the firewall gets penetrated by the end of the fuel rail and cuts in to the wires within. See pics.


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HI Sidewinder!

Thanks for the really helpful response. I'll back-probe the connectors and see what is there. The 5V I measured was with an "open" connector (I.e. probing the front of the connector, disconnected from the sensor). I'll also check the loom back there at the fuel rail.

Does that mean we agree that this is likely an electrical issue vs. some sort of actual mechanical problem? I was starting to ponder water pump and t-stat replacements, and then had the thought that if they shared a bus or a ground it could be electrical.

S

rwmtn80y said:

HI Sidewinder!

Thanks for the really helpful response. I'll back-probe the connectors and see what is there. The 5V I measured was with an "open" connector (I.e. probing the front of the connector, disconnected from the sensor). I'll also check the loom back there at the fuel rail.

Does that mean we agree that this is likely an electrical issue vs. some sort of actual mechanical problem?

Yes.

I was starting to ponder water pump and t-stat replacements, and then had the thought that if they shared a bus or a ground it could be electrical.

S

Click to expand...

What was the color of the wire(s) you probed to find 5 volts?

Hi Sidewinder - you nailed it. Fuel rail into the loom, pulled it off the rail, and taped it - voila both errors fixed. You are awesome!