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 (TJ) (WJ) (RS) (XK) (WK) (RS)
Concern: Loud noise/vibration from interior fan (for A/C heat)(HVAC) especially when on high speed, usually speed 3 or 4.
Cause: HVAC fan (blower motor) is out of balance. Usually caused by fan sucking in leaves or other debris.
Resolution: Remove the blower motor and inspect/clean the fan blade (squirrel cage type). Normally the blower motor is located under the passenger side dash. Most are easy to remove, held in with 3 screws, either Phillps or T20 torx.
Vehicle: Jeep Wrangler (TJ) approx 1997-2002
Concern: The check engine light is on. Scan tool shows a fault code for the TPS (throttle position sensor) circuit. The fault is always present and is not able to be cleared. Typical repair methods have been unsuccessful (you can't fix it).
Cause: If the clockspring ribbon shorts out in a certain way, due to the circuit complexities inside the PCM, the PCM sees this condition as a TPS circuit fault. This was likely an unforeseen circumstance during the engineering phase.
Resolution: Stop whatever you are doing. Hopefully you have not replaced very many expensive parts yet. Remove the two steering column covers and disconnect the connectors going to the clockspring. Retest for the TPS fault.
Vehicle: Jeep Wrangler (TJ) with 4.0L engine
Concern: Loss of power. Engine feels like it is producing only about 50% of normal power. Engine runs smoothly and idles normally.
Cause: Insulation pad (attached to underside of hood) was drooping down and covering the air inlet to the air filter. Reduced airflow to engine caused the power loss.
Resolution: Remove part of the the hood insulation pad closest to the air filter box.
Details: This was a very interesting case. Another dealership had been working unsuccessfully on this vehicle. They had replaced many parts, including the whole engine! Most Wranglers are not equipped with a hood insulation pad, however, this particular vehicle was.
Vehicle: 2006 (TJ) Jeep Wrangler
Concern: The MIL is on. Scan tool reveals DTC P0301 cylinder 1 misfire and P0300 multiple cylinder misfire. The engine seems to be running normally. Found a related symptom later: after vehicle sits for a few hours, it has a long crank time.
Cause: The fuel pump had an internal leak. The fuel pressure was dropping to -0- after the engine was shut off.
Resolution: Test fuel pressure and replace the in-tank fuel pump assembly.
Details: The leak was allowing air to enter the fuel line, which caused a cold-start misfire. This is a perfect example of why it is important to "analyze the symptoms" and "look at the big picture." In this case, the customer did not complain about the extended crank time, but it turned out to be a contributing factor.
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: 2006 -2007 Jeep Wrangler (TJ)(JK) with manual transmission (NSG370)
Concern: Customers report a squeal-like sound while clutch out. Appears to be coming from transmission. Squeal stops when clutch is depressed.
Cause: Incorrect pre-load on clutch throw-out bearing.
Resolution: There is a TSB (06-002-07) for this issue. On the TJ - replace the Rod and Clutch Slave Cylinder Actuator. On the JK - replace the Washer, Spacer, Lubricant (Mopar Manual Transmission MS-9224), Adhesive, Stud N' Bearing Mount, and the Throw-out Bearing.
Details: TSB #06-002-07