SES on because of 2 codes-

[jcono]

Hello again,
Well good old Autozone did me a solid by finding 2 reasons why the SES lite won't go off.

Codes P0171, which I guess is usually 1) MAF 2) O2 sensor 3) ignition misfire or 4) fuel injector problem.
If it helps, the engine is running very smooth so I'm thinking it's not a ignition misfire.

Second code is P0128, which many of you are familiar with. Coolant level warning light was coming on recently so I added a little. The light doesn't come on anymore but that was a few weeks ago and I figure it shouldn't still be throwing this code. So the Thermostat must be the culprit.

I guess my main question concerns P0171- can I asume it's the O2 sensor?

Thanks in advance for your help!
Jan


I have a '03 AWD V6 with about 130,000 mi. I should add.

[fdryer]

DTC P0128 Coolant Thermostat

DTC P0171 Fuel Trim System Lean Bank 1

The coolant low level light is a separate issue to the P0128; one turns on an indicator while the other turns on the SES light with a code. Totally separate problems. If you can see a live scan of coolant temperatures, you'll verify whether or not replacing the thermostat is needed. In the meantime, for the winter, you can go old school and simply block off part of the radiator sufficiently to raise radiator temperatures to aid heat retention, possibly avoiding the P0128 from returning until warmer weather returns. Then you can decide on replacement.

Running lean on one cylinder bank can be from several issues; the O2 sensor, a leak in the intake system to that bank, worn plugs, etc..

At 130,000 miles has the timing belt, water pump, spark plugs, and fuel filter been replaced when 100,000 miles came up? A worn timing belt not replaced may allow cam timing to slip and cause the lean bank of cylinders. Some have reported the old belt looking new but that may be an exception to the rule. Others replaced their belts only to have it slip and cause mistiming problems later with headaches troubleshooting misfiring, lean conditions in one or both cylinder banks until re-checking belt timing. Mistiming during belt replacement.

[jcono]

The timing belt, plugs, water pump and fuel filter were all done at 100K.

I will try the old cardboard in front of the radiator trick. It has been pretty cold here in NJ lately.

Thanks again!
Jan

[VTchemist]

My rear O2 sensor went bad. The dealership read the code with their system. It told them which of the (4?) sensors was bad.

I am not sure if AutoZone's scanner can discern which sensor is bad.

Suggest you go to the dealer unless you can confirm which sensor is bad. You could replace all of them, but you still may not solve the problem (if it's something else).