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post #1 of 8 Old 09-13-2021, 07:37 PM Thread Starter
philbone
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Errors plus incorrect temperature readings

I am a newbie here and hope that it is ok to post my problem in this thread... I think it is relevant.
Vehicle is a 2013 Jeep GC Laredo 5.7 Hemi
We have had plenty of the typical cooling issues with it in the past:
Leaky water pump, bad thermostats etc - all been fixed...

This one has me stumped. CEL came on and the engine temperature refuses to show anything above about 148 degrees, even though the engine is measuring about 200 with an IR temperature gauge. It threw the following...

P0128 code... Here is what I have done...
- Checked coolant for level and purity (replaced a year ago together with water pump)
- Checked thermostat using IR gauge; at about 160 the top hose starts to carry very hot coolant (Thermostat was also replaced a year ago with a Mopar OEM)
- Replaced ECT sensor (after testing resistance changes with heat / cold)
- Bled system and double checked bleed valve.

So the temperature gauge reads colder than it is, and the digital reading in the instrument cluster reads <100. It understand that it is always reading "cold" which is why it is triggering the error. Today it also threw P0118.

- I checked the wiring to the ECT sensor - one wire has 5v DC, the other I am not sure how to check back to the computer (I don't have a wiring diagram)

What else could it be?

Please help and THANK YOU !!!

Phil

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post #2 of 8 Old 09-13-2021, 08:55 PM
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1st I gotta ask - jeep is STOCK - powertrain no BS programmers, chips, add on's modifications?

Start with the p0118* a issue with ECT sensor voltage. Trouble tree has the procedure.

Might be interesting, after sitting overnight using a scanner with KOEO check ECT, IAT and ambient temp readings - (oil temp if applicable) They should be close my thinking is you might find that @100 difference.


*Code P0118 : Engine Coolant Temperature Sensor 1 Circuit High
one wire 5v other ground to PCM shared

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 8 Old 09-13-2021, 11:02 PM Thread Starter
philbone
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Thank you for the reply,

Indeed, vehicle IS stock.

I will try to find Trouble Tree's procedure. I am pretty sure that I get it - 5vdc to the ECT and a voltage drop dependent on temperature to the thermistor. To which terminal does the return wire connect on the ECU? I could also check for short/ ground from that wire when the ignition is off.

So many people have told me to just change the thermostat (yet again) - but it does seem to be working correctly. If I do should I use a Mopar again? Any other aftermarket thermostats any good (203 degrees)

The big confusion to me is that the cluster temperature gauge reads <100 when the actual temperature of the engine is more like 200 degrees when measured with an IR thermometer at the ECT housing.

Phil
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post #4 of 8 Old 09-14-2021, 12:37 AM Thread Starter
philbone
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UPDATE!

Ok... I think I might have found something going from your trouble tree list of diagnostics...

Connections to the ECT sensor...
- One wire has 5 vdc
- the other (signal) registers 6.4 ohms to ground - virtually a short!

I have no idea how that wire is routed and to where it goes (on the ECU) How would you go about trying to trace it and find the problem? Would it be a replacement of the harness or is a repair possible?
I am pretty good with electronics.

Many thanks again,

Phil
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post #5 of 8 Old 09-14-2021, 12:25 PM Thread Starter
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Update #2

So after a little research... I realize that of the two wires going to the ECT, one "signal wire" carries the voltage and the other is supposed to go to ground. The PCM gets its signal voltage from the voltage wire, with reference to the reference voltage as part of a voltage divider circuit. (So please ignore my misinterpretation earlier that the one wire should not be grounded.)

So here is what we have:
ECT sensor - good
Thermostat - good
Coolant level and bleed - good
Wiring - good
No shorts
PCM / ECU - good (otherwise we would not detect any voltage whatsoever)

So the final problem is that both the temperature gauge and the digital temperature readout in the cluster both indicate a temperature of less than 100 F when the engine is running and registered an actual measured temperature of about 190 using an external thermometer.

THEREFORE...

I think the only thing left is that the vehicle's computer needs a reprogram / reset.

Does anyone concur? and if so does anyone know what is involved? I am thinking this may require to be a visit to the Jeep service, who here in Las Vegas are notoriously not a great experience.

I hope that this thread proves useful to anyone else and thank you for your time.

Cheers

Phil
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post #6 of 8 Old 09-14-2021, 01:58 PM
jtec
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My comment 'might be interesting' was a check of gauge display temp to known temp (ambient) after sitting overnight. All the temp gaugess should be @ the same and that is ambient. I think the ECT will be way off other gauges and off from ambient.

Do you have the jeep P0118 trouble tree?
Also I did not ask before, Do you have a SCANNER to view data?
Sometimes you gotta communicate with these animals.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #7 of 8 Old 09-14-2021, 03:55 PM Thread Starter
philbone
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Yes I do have a scanner... it is showing a graphing temperature at the ECT sensor of 40F !! It is flat-lined and does not move from this over a 10 minute warm up.
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post #8 of 8 Old 09-14-2021, 07:23 PM
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what about the other sensors - first thing in the morning - I am curious if they are all close.
reason a shared ground.

hope these help -
Attached Files
File Type: pdf 1 p0118 edut.pdf (216.8 KB, 0 views)
File Type: pdf 2_p0118 edit.pdf (273.2 KB, 0 views)
File Type: pdf 3_p0118 edit.pdf (201.1 KB, 0 views)

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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