The #1 cause of XJ no-start. CPS dies hot, may restart cold. Bolted to the top of the bellhousing with two T-30 torx. Always carry a spare.
The Crankshaft Position Sensor is the most common single failure on the 4.0L XJ and the top reason for a sudden no-start. Symptoms: vehicle runs perfectly until shut off after a long drive, then refuses to restart while hot. After 30-60 minutes of cooling, restarts and runs again. No check engine light necessarily. Some failure modes throw P0320 or P1391 on OBD-II. The sensor lives on the top of the bellhousing where the transmission meets the block, on the driver side. Two T-30 torx bolts hold it. Wiring connector is a three-pin plug that often becomes brittle. Beware of cheap aftermarket sensors - Standard SC107, Mopar 56041820, and Bosch are reliable; off-brand units sometimes fail in the box. Renix 1987-1990 uses a different sensor (mounted in the bellhousing same area). Carry a spare in your trail kit - this is the single highest-payoff spare part for an XJ. Replacement is a 15-minute job once located. The bolts strip easily; use a quality 6-point torx bit, not a 12-point.
| Part | Vendor | Est. price |
|---|---|---|
| Mopar CPS (1991-2001) | Mopar/RockAuto | ~$45 |
| Standard SC107 | RockAuto | ~$30 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.