Vehicle: All Chrysler/Jeep/Dodge (LH) (CS) (PT) vehicles equipped with NVLD (natural vacuum leak detection) system.
Concern: The check engine light is on. Scan tool reveals code (DTC) P0440 general evaporative system failure.
Cause: Usually caused by a failure of the switch inside the NVLD assembly.
Resolution: Replace the NVLD assembly to correct.
Details: The purpose of the NVLD system is to test the integrity of the fuel vapor containment system. For example, if the fuel filler cap was not in place, or there was a leak in the fuel tank/vapor lines/canister, the NLVD system would identify the fault and the PCM will illuminate the check engine light. This system is mandated by the EPA, to prevent evaporative emissions. All recent vehicles have this system in one form or another. Evaporative emissions are caused when gasoline evaporates into the atmosphere, which is a form of pollution. This also explains why the nozzles at gas stations have changed over the years---to prevent evaporative emissions. The NVLD system does not test the integrity of the pressurized fuel lines or fuel injectors. Note: P0440 indicates a general fault with the NVLD system. It does not neccessarily mean that there is a leak.
Vehicle: All vehicles. (JK)(ZJ)(CS)(JC)(TJ)(XJ)(PT)(KJ)(KK)(KA)(AN)(ND)(DR)(DS)(WJ)(WK)(XK)(LX)(LH)(FJ)(JR)(JS)(RT)(RS)(NS)
Concern: The MIL (check engine light) is on. The scan tool reveals DTC P0601 PCM internal controller failure.
Cause: The PCM (engine computer) has an internal fault.
Resolution: Replace the PCM to correct.
Details: This is an easy diagnosis. When P0601 is present, the solution is always to replace the PCM. There is no other possible cause. Normally the vehicle is still driveable.
Vehicle: All Chrysler, Jeep, and Dodge vehicles. (JK)(ZJ)(CS)(JC)(TJ)(XJ)(PT)(KJ)(KK)(KA)(AN)(ND)(DR)(DS)(WJ)(WK)(XK)(LX)(LH)(FJ)(JR)(JS)(RT)(RS)(NS)
Concern: Alternator failure. The alternator (generator) is not charging. Electrical problems.
Resolution: Hold on for a minute. Alternator failures are extremely rare on Chrysler, Jeep, and Dodge. You need to rule out the battery, wiring, and PCM first before replacing the alternator.
Details: The alternator is controlled by the PCM (engine computer). Again, true alternator failure is very rare. In ten years as a dealer service dept tech, I have replaced maybe five alternators.
Vehicle: 2004 (LH) Chrysler 300M front wheel drive 3.5L (had 150,000 miles)
Concern: Engine will not idle properly. Have to press accelerator to keep engine running. Engine stalls due to idle problem. Engine runs normally otherwise. No check engine light. Related symptom: The engine cranking speed was a bit low.
Cause: The IAC (Idle Air Control) valve was failing. It was able to influence the idle speed but not control it very well.
Resolution: Replacing the IAC valve totally resolved the problem. Initially I figured the slow cranking speed was related. The battery was original(!) and failed according to the battery tester with about 200 CCA of a 600 CCA rating. Replacing the battery got the cranking speed up to normal, but actually made the idle problem worse due to the engine computer memory loss when the battery was disconnected.
Details: On some vehicles, low cranking speed due to a bad battery causes idle problems. Not in this case. The IAC valve is located on the passenger side of the throttle body, under the throttle position sensor. The throttle body is at the rear of the intake plenum on 3.5L.