Oil Temp sensor wiring harness issues

SonicVQ

I checked the triple meter wiring diagram and it is isolated from the engine oil temperature circuit. The ECM reads the oil temp and sends it to the triple meter via the CAN bus.

I am starting to suspect the ECM

The engine oil temperature circuit (and every other ECM sensor input) uses 5 volts.

Is it possible when the wires melted the bare 12v alternator wire touched the bare oil temp wires? If that happened, 12 volts would have been sent to the 5 volt sensor input.

We know the 5 volt supply is good, as you measured almost 5 volts with the sensor unplugged. AND the ground is good, since you had 0 volts.

The engine oil temperature circuit inside the ECM connects to a "multiplexer" (multiple inputs with a single programmable output) before it goes to the analog to digital converter in the main CPU (actually a SH7059 32 bit RISC microcomputer) I suspect one of those two items may be damaged.

OilLeaks

I have an EcuTek tune, so I can see all the parameters. It always reads 275 degrees regardless if its cold or hot. I have an ECU on the way so I can test it & see. I'd almost rather it be the ECU because that's easier than tracking down unknown electrical gremlins. 😐

Rusty

It's reading 275F. It should be close to limp mode. It's pulling a whole bunch of timing. The ECU starts to pull timing around 240F. The higher it goes, the more it pulls until limp mode.

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OilLeaks

The false high oil temp is causing the throttle bodies begin to close under boost in higher rpm & drop to 50% in between shifts. Hopefully I can get it resolved soon. Feels like a stutter on accelerating

SonicVQ

Can you modify the Oil Temp map?
If you can, you could temporarily re-map the high temp to a lower temp and see if the engine runs better.

I know on ECUTek you can:
(Stock map from the top is: 205, 191, 124, 110, 99)

Attached Images

oi.jpg (168.8 KB, 45 views)

OilLeaks

My tuner tried doing that. It wouldn't let it happen. I think it's a safeguard...or the ECU simply can't read the sensor voltage.

SonicVQ

As far as I can see, I think everything else has been ruled out.
I look forward to your update.

OilLeaks

**UPDATE**
So I figured out the problem. I swapped the ECU & still got the same high oil temp reading even though I got the proper readings of 5v on the green wire and 0v on the black wire. I decided to do a little more investigation. As it turns out, there was no continuity in the black wire. I replaced that wire and everything started working again. I guess when the previous owner did a repair he didn't do it properly. Apparently, the ECU will default to a high temp reading if the sensor isn't working. I doubt anyone else will have the same problem, but if they do, hope this helps!!

SonicVQ

Good news!

However, the reason the ECM showed a high temp, was because of bad wiring.

The engine oil temperature sensor (and the coolant temp sensor) decrease in resistance as warms up, and increases in temperature as it cools. This is known as a negative temperature co-efficient sensor (NTC)

Since the ECM reported a very hot temp, the resistance it saw was very LOW, like a partial short to ground.

When the sensor is cold, the resistance is very high. If the sensor is disconnected, it will show as -40, because with the sensor being removed is a (very) high resistance.

Anyway, I'm glad you got it all sorted out!
Thanks for the update.