Fuel trims

Post by **pkc303** » 30 Nov 2015, 14:41

My fuel trims stopped working on scan tool. Car running rich. Temp sensor replaced with Volvo part. All worked well for an hour, then the temp gauge went to zero and lost fuel trim readings. Obd2 shows coolant temp at 195 F.

What controls fuel trim, other than Coolant Temp Sensor? I suspect MAF?

Any thoughts?

Post by **misha** » 30 Nov 2015, 14:50

Check connectors for ECT,they corrode with time and usually,cleaning always helps.
The same ECT feeds both...instrument cluster and ecu.

Also,check if wires are not shorted or cut.
Temp gauge behaviour indicate that you lost connection with ect.

Post by **pkc303** » 30 Nov 2015, 15:12

Will check tonight. Where is(are) the connection(s)?

Post by **erikv11** » 30 Nov 2015, 18:13

ECT mounts into the thermostat housing, the thing with the black wire coming out of it. There is a short wire from the ECT to a black connector, give that a look. Sometimes the connector disintegrates, sometimes the metal connectors corrode, sometimes both.

Post by **misha** » 30 Nov 2015, 18:43

pkc303 wrote:Will check tonight. Where is(are) the connection(s)?

You should know that since you replaced it with Volvo part.

Post by **Rondo** » 30 Nov 2015, 19:28

[quote="pkc303]

What controls fuel trim, other than Coolant Temp Sensor? I suspect MAF?

Any thoughts?[/quote]

O2 sensors also control fuel trim, from what I've read, especially the rear. When I replaced my cat with an aftermarket, my fuel trim was way off. I installed a spacer to get the sensor back to factory depth in the exhaust stream and was back to normal.

Post by **pkc303** » 30 Nov 2015, 20:12

It could, but Imwould expect a code with it. No codes.

Post by **Rondo** » 30 Nov 2015, 20:50

Mine threw no code at all, but that may be because the sensor was actually working, just the fuel/air mix was off.

Post by **erikv11** » 30 Nov 2015, 21:06

Front O2 yes, rear O2 no.

Rear O2 on a P80 is strictly an emissions tattle tail, it has no role in fuel trims. It just reports what is happening in the cat, either turns on the CEL or not, no other function.

Post by **pkc303** » 01 Dec 2015, 07:25

Reseated the ECM, seems to work, on the short drive, will try a longer one soon.