Power Door Lock and Keyless Entry System -- Description and Check

Contributed By: Bill Kelsey

From the Haynes manual, section 12-26: Power door lock and keyless entry system -- description and check.

1. The power door lock system operates the door lock actuators mounted in each door. The system consists of the switches, actuators, relays and associated wiring. Diagnosis can usually be limited to simple checks of the wiring connections and actuators for minor faults which can be easiliy repaired.
2. Power door lock systems are operated by bi-directional solenoids located in the doors. The lock switches have two operating positions: lock and unlock. On later models with keyless entry the switches activate a relay which in turn connects voltage to the door lock solenoids. Depending on which way the relay is activated, it reverses polarity, allowing the two sides of the circuit to be used alternatively as the feed (positive) and ground side. On earlier models without keyless entry the switches directly activate the door lock motors.
3. If you are unable to locate the trouble using the following general steps, consult your dealer service department.
4. Always check the circuit protection first. On these models the battery voltage passes through the 30 amp circuit breaker located in the passenger compartment fuse block.
5. Operate the door lock switches in both directions (Lock and Unlock) with the engine off. Listen for the faint click of the door lock solenoid (motor) or relay operating.
6. If there's no click, check for voltage at the switches. If no voltage is present, check the wiring between the fuse block and the switches for shorts and opens.
7. If voltage is present but no click is heard, test the switch for continuity. Replace it if there's no continuity in both switch positions.
8. If the switch has continuity but the solenoid or relay don't click, check the wiring between the switch and solenoid or relay for continuity. Repair the wiring if there's not continuity.
9. On later models if the relay is receivning voltage from the switch but is not sending voltage to the solenoids, check for a bad ground at the relay case. If the relay case is grounding properly, replace the relay.
10. If all but one lock solenoids operate, remove the trim panel from the affected door and check for voltage at the solenoid while the lock switch is operated. One of the wires should have voltage in the Lock position; the other should have voltage in the Unlock position.
11. If the inoperative solenoid is receiving voltage, replace the solenoid.
12. If the inoperative solenoid isn't receiving voltage, check for an open or short in the wrie between the lock solenoid and the relay.

NOTE: It's common for wires to break in the portion of the harness between the body and door opening (opening and closing the door fatigues and eventually breaks the wires.)

Hope this helps.

Bill Kelsey
Aberdeen, SD
'79 widetrack Cherokee "S"