penicholson

I'm getting a coolant sensor intermittent error code:

16501 - Engine Coolant Temp. Sensor (G62): Signal too Low
P0117 - 35-10 - - - Intermittent

I've replaced the sensor and still get the code. When I unplug the sensor the reading is still intermittent, it should from what I understand go to around 140 C. I'm thinking I have a harness problem or a ECU problem.

Where can I find a wiring diagram? If not available on line, is it available in the Bentley service manual, or do I have to get a Bentley wiring manual?

Are schematics of the ECU available?

Paul

4Driver4

Are you sure you replaced the right sensor?

penicholson

The online knowledge I've seen indicates it is the sensor behind the engine on the passenger side. It was a coolant sensor as some coolant came out when I removed it.

Is there another coolant sensor hidden somewhere else?

penicholson

It looks like the connector to coolant sensor connection is intermittent.

Does anyone know how to pop the pins out of the connector?

4Driver4

Sounds like you got the right one. Is the connector snapped on tight?

penicholson

Yes the connector is snapped on tight.

I've taken readings on the sensor and on the connector with them disconnected from each other.

The coolant temp sensor reads 840 ohms from pins 1 to 2 and 1920 ohms from pin 3 to 4.

WIth the ECU off, connector pins 2 and 3 are connected to ground albeit with a bit of resistance, 2.3 and 5.1 ohms respectively.

When the ECU is running pin 1 of the connector has a 0 to 5 volt pulsing signal on it. I wonder if the device that is reading it takes two readings, one reading when the signal voltage is applied to measure the resistance and the other reading when the signal is not applied to measure the DC offset of the ground return so it can be removed as an error source.

Pin 4 has 100 mV on it. This seems too low. I have traced pin 4 to pin 93 of the ECU. I suspect that pin 4 should have a similar signal to what is on pin 1.

Do you know why there are two sensors in this sensor? Is one for the dashboard instrumentation and the other for the ECU?

4Driver4

Yes.

penicholson

The ECU is OK. PIn 93 has a 5 volt bias signal for the coolant temp sensor. Connecting a resistor to ground sets a stable reading on the VAGCom.

There is a short to ground in the wiring harness. With the ECU disconnected the reading to ground on ECU connector pin 93 fluctuates between an open circuit and a couple hundred ohms to ground. Pushing on the harness makes the short come and go.

The harness is swaddled in tubing, tape, and rubber. It goes everywhere. Does not look like fun to repair or to replace.

Suggestions?

penicholson

The engine wiring harness was abraded where it rested against the firewall behind the right looking aft side bank of cylinders. One wire was intermittently shorting against the firewall where the paint was worn away. A bit of electrical tape and duct tape and it's working again.