Code
B1818
Other
B — Body
Wiper Rear Motor Up Relay Coil Circuit Failure
AI status
Completed
Completed
100%
Causes
- Blown fuse protecting the rear wiper circuit
- Failed rear wiper relay (coil open or shorted)
- Broken, corroded or disconnected wiring in the relay coil circuit
- Poor or missing ground at relay or BCM
- Faulty connector pin (corrosion, bent, pushed out)
- Control module/BCM driver failure or software fault
Symptoms
- Rear wiper does not operate or operates intermittently
- No clicking of the relay when rear wiper is commanded
- Rear wiper stuck out of park or fails to return to park
- Related warning or body control fault messages on dash
- Possible blow of fuse when attempting to operate rear wiper
What to check
- Read and record all stored codes and freeze frame data from BCM
- Visually inspect fuses, relay, relay socket and associated connectors
- Wiggle wiring harness while operating wiper to look for intermittent faults
- Check for corrosion, bent pins or water intrusion at connectors
- Measure supply voltage and ground at the relay socket with key on
- Measure relay coil resistance and compare to specification or expected range
Signal parameters
- Relay coil resistance: typically tens to a few hundred ohms (refer to service manual); open or infinite indicates open coil
- Coil supply voltage: ~12 V (battery voltage) present at relay supply terminal with key on
- Control/trigger voltage: either ~12 V or switched ground when activated (depends on design)
- Ground continuity: low resistance (
- Activation behavior: relay coil should energize and click when commanded; measured coil current typically
Diagnostic algorithm
- Verify: Clear codes, then attempt to operate rear wiper and confirm B1818 returns. Note any additional codes.
- Visual inspection: Check fuses, relay, relay socket, BCM connectors and wiring for damage or corrosion.
- Relay verification: Remove relay and bench-test coil with 12 V supply (observe click). Measure coil resistance with a multimeter; infinite indicates open coil.
- Power/ground check: With harness connected, measure battery voltage at relay supply terminal and continuity to ground. Repair any missing supply/ground.
- Control signal check: Backprobe control/trigger terminal and operate wiper switch; verify expected control signal (voltage change or ground switch).
- Wiggle test: With connector back-probed, wiggle harness and connectors while activating to identify intermittent faults.
- Trace wiring: If control or supply missing, trace harness from relay to BCM looking for opens, shorts, chafing or water damage. Repair or replace damaged wiring or connectors.
- Module check: If wiring, relay and motor check good, test or substitute BCM/relay driver (follow manufacturer procedures).
- Motor/mechanical check: If electrical checks are normal but high current or odd behavior observed, inspect/replace rear wiper motor and linkage.
- Verify repair: Reinstall components, clear codes, exercise system through several cycles and road test. Confirm code does not return.
Likely causes
- Open or high-resistance relay coil or relay socket
- Damaged harness between BCM and relay (chafing, broken conductor)
- Corroded connector at relay or wiper motor harness
- Missing supply or ground to the relay coil
- BCM output transistor or driver circuit fault
Fault status
Status
WIPER REAR MOTOR UP RELAY COIL CIRCUIT FAILURE — circuit open/short or abnormal coil resistance detected; relay or wiring fault suspected.
Repair difficulty: Medium
Diagnostic time: 0.5-1.5 hours
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