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.
- 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
- 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
- If you are unable to locate the trouble using the
following general steps, consult your dealer service
- 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.
- 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.
- 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.
- 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.
- 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
- 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.
- 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.
- If the inoperative solenoid is receiving voltage, replace
- 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.
'79 widetrack Cherokee "S"