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How do I fix trouble codes P0171 and P0118


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Hello scotty and staff, I have two codes on my 2007 toyota matrix.


Codes are p0171 and p0118


If anyone can help me explain what they mean and what can be done to fix it.


Thank you.

3 Answers

The way the P0118 dtc gets set is the computer sees a voltage so high on the ECT sensor circuit, for at least 1/2 a second, that it has to be an Open in the circuit. 

This is almost always caused by a bad ECT sensor. (the code can also be set if there's a break in the ECT sensor wiring or a bad ECT sensor wiring connector ((causing an Open in the circuit)) but that's typically not the reason)).

If you have a scanner you can look at the Freeze Frame data (ECT sensor) from when that P0118 code was set. It will probably read -40°F

That's because the higher the voltage that the computer reads on that circuit equals the lower the engine coolant temperature and an Open in that circuit will cause the computer to read the maximum voltage. In this circuit it's 5 volts. The P0118 code says ECT sensor voltage high

This is a case where you'd be pretty safe by replacing the ECT sensor.

If you have a cheap scanner and you want to check the integrity of the wiring and the connection to the PCM you could disconnect the wiring connector at the ECT sensor. Grab a paperclip and jump the 2 terminals on the connector. Turn the ignition Key to ON, go to Live Data and look at the ECT sensor temperature. If the wiring is OK the temp will be maxed out at around 284°F. (you're pulling the 5 volt reference down to Ground and forcing a low voltage condition on the circuit).

Anyway, the thing to keep in mind is that while the P0118 dtc is present the computer isn't using the voltage input from the ECT sensor. It's defaulting to some preprogrammed engine temperature value so you should clear that code while you're deciding what you're going to do (maybe it won't come back ((for a while)).

Also, that P0171 dtc is an air/fuel mixture being too Lean code but you wouldn't address that code without resolving the P0118 code first because the computer is ignoring the ECT sensor with the P0118 code present and that's going to throw off the air/fuel ratio especially before the engine reaches operating temperature.







It took about 30 seconds to find the following with a web search:


You can easily look what they mean on the web (or this forum). I certainly can't memorize 6,783 codes.