[CREWZIN]

It looks like your gonna need further diagnostic work to pin point the problem.


P0138 O2 Sensor Circuit High Voltage (Post Catalyst)

P0172 System Too Rich

Oxygen sensors can set trouble codes for various reasons. An open sensor wire can set trouble codes. If a sensor stays lean or rich for a long period of time, lean or rich codes may set. In either case, the sensor may be at fault. Before condemning the sensor, there are some very important checks that should be made.

For continuously rich O2 sensor readings:

1. Check the fuel pressure. High readings will cause rich conditions.

2. Leaking injector(s) will cause rich exhaust.

A leak down test and/or a power balance test can usually reveal the leaker.

3. A contaminated or malfunctioning canister purge system can very easily put uncontrollable amounts of fuel into the intake manifold. Simply disconnecting the vapor hose can reveal this as your problem system.

4. Check vacuum to voltage readings at the MAP sensor. A low MAP output will cause a rich ecu reaction. (Don't forget vacuum readings again!)

5. A false tps signal can cause the system to go rich if the Ecu sees a high tps output. Check tps readings at idle and for a smooth rise to wide open throttle.

Remember that the O2 sensor can help you simplify your diagnosis and help you avoid frustration!