Vehicle: 1993-1998 (ZJ) Jeep Grand Cherokee with 4.0L engine, 1999-2004 (WJ) Jeep Grand Cherokee with 4.0L engine, 1997-2001 (XJ) Jeep Cherokee with 4.0L engine, 1997-2006 (TJ) Wrangler with 4.0L engine.
Concern: Engine cranks but will not start. May have died while driving. Related symptoms: Fuel gauge shows 'empty', however the fuel tank is not empty. Volt gauge is all the way to the left (low), but the battery is not discharged.
Cause: The CKP (crankshaft position) sensor is shorted internally. Turn the key off. Unplug the CKP sensor and retest for proper gauge operation.
Resolution: Replace the CKP sensor to correct.
Details: Scan tool will show 'no response' to PCM (engine computer). This is why the fuel gauge and volt gauge are inoperative. The PCM is not functioning, so the fuel and voltage data is not bussed to the instrument cluster. When the the CKP sensor shorts internally, the PCM will not function. The connector is located on the right side of the engine, near the rear of the engine block. The CKP sensor is located on the left side all the way in the back. Usually it must be replaced from under the vehicle. This is a fairly common problem.
Vehicle: All vehicles (ZJ) (LX) (XJ) (RS)
Concern: No start. Engine cranks but does not start. Most likely the engine died while driving. The fuel gauge shows 1/8 of a tank.
Cause: The fuel tank is totally empty. The fuel level sending unit is failing.
Resolution: Replace the fuel level sending unit, or the entire fuel pump assembly. Add fuel.
Details: Always start with the basics.
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.