Cycle key ON-OFF-ON-OFF-ON within five seconds. CEL flashes two-digit codes. No scan tool required.
For 1991-1995 HO XJ (non-OBD2), Chrysler implemented a clever code-flash diagnostic: cycle the ignition key ON-OFF-ON-OFF-ON within five seconds, leaving it ON. The Check Engine Light then flashes stored codes as two-digit numbers. Count short pause vs long pause: a pulse-pause-pulse equals 1-1 (code 11, no CKP signal); pulse-pulse-pause-pulse-pulse-pulse-pulse-pulse equals 2-5 (code 25, IAC valve), etc. Code 55 ends the sequence (no more codes). Common XJ codes: 11 (no crank signal), 12 (battery disconnect), 17 (engine cold too long), 21 (O2 sensor), 22 (CTS), 24 (TPS), 25 (IAC), 27 (injector), 31 (purge solenoid), 33 (A/C clutch), 41 (alternator field), 42 (auto shutdown relay), 51 (lean fuel), 52 (rich fuel). Renix-era (1987-1990) uses a different method entirely (jumper at the C-101 connector, see separate entry).
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.