QuestionRoland, I have a Chrysler Sebring Coupe and the check engine lite came on. I scanned the code and received a P0171 system too lean. What are some common causes for this conditoin that I can check? I have good mechanical experience restoring older cars, but need some guidance on the new ones. Thanks...
AnswerHi Charlie,
One interesting aspect is that the code is specific for the rear cylinder bank and is based upon its upstream O2 sensor not being happy with the mixture. On the coupe there are a pair of sensors on each bank whereas on the convertible there is only sensors on rear bank (ref. 2.5L 1998 powertrain manual). The list of possible causes is legion:
ignition coil, powertrain control module, engine parts tolerance, puel pump, fuel pump inlet filter, ignition secondary wires, low fuel level, injectors stuck closed, MAP sensor, O2 sensor (upstream), fuel pressure regulator, fuel pump relay, spark plugs, wiring harness connectors.
Most of these are not unilaterally inclined so I wonder if one should look at only those that affect just the rear bank or look at all of them?
Interestingly, if you then look at the decision tree it says to take these steps in order:
Check fuel pressure, make sure fuel level is at least 1/4 full (did the car run out of fuel when the code was logged), check out other fault codes first, with engine warmed check for leaks between engine and O2 sensor, check if the 02 sensor is switching between lean and center and rich at least twice in 20 seconds (that is normal), if you have a DRB see what is the long term adaptive memory % value.
Then check secondary ignition with a scope, spray wires and observe scope, disconnect plugs one at a time observe scope, is secondary voltage at least 25kv.
Then check the coolant temp sensor (is it 7 to 14K ohms at 70F and 700 to 1k at 200F).
Then check the MAP sensor and see if it changes
signal and is accurately measuring the vacuum (tee in a vacuum gauge).
Then do typical check for engine mechanical:
read vacuum at idle, valve timing, engine compression, camshaft lobes, check crankshaft sensor slots for debris/deterioration, check exhaust system for restrictions, check PCV system, check drive sprocket timing, check torque converter stall speed, check for power brake vacuum leaks, no contamination of fuel, check for plugged or restricted injector or crossed wires thereto, check the resistance vs temp of intake air temp sensor (spec similar to that of coolant sensor).
I wish it were more specific, but that is how it is treated in the '98 manual for that 2.5L engine. I would be interested to know if you find the correct cause of the code.
Roland
