B1816

Code

Other B — Body

Wiper Rear Motor Down Relay Coil Circuit Short To Battery

Brand: Other

Type: B — Body

Views: UK: 23 EN: 29 RU: 43

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Short to battery (chafed wire, pin pushed out and touching positive, pinched harness)
Failed relay with internal short between coil and supply
Corroded/bridged connector or terminal at relay, harness, or rear wiper motor/module
Faulty BCM / body control module or relay driver transistor stuck high
Aftermarket accessories or recent repairs that disturbed wiring

Symptoms

Rear wiper does not park/move correctly or does not operate
Intermittent or constant rear wiper operation
Related wiper fuse blows or other electrical anomalies
DTC B1816 set and possibly stored with related wiper codes

What to check

Scan for DTCs and freeze frame data; note conditions when the code set
Visual inspection of relay, relay socket, fuses, rear wiper motor connector and harness for damage, corrosion, or water intrusion
Remove relay and inspect coil terminals and socket for melted pins or bridged contacts
Measure relay coil resistance with multimeter (compare to spec) and swap with known-good relay of same type if available
Backprobe relay coil terminals with ignition ON to check for unexpected battery voltage on control circuits
Disconnect rear wiper motor/module connector — see if code clears or behavior changes to isolate upstream/downstream

Signal parameters

Normal: No constant battery voltage on relay coil control circuit when relay is OFF; only one coil terminal should have battery (feed), the other is controlled by module (switch to ground) when activated
Coil resistance (typical): ~40–200 ohms for many small relay coils (vehicle-specific — consult OEM specs). A reading near 0 ohms indicates a short; infinite indicates open coil
With ignition ON and relay removed: battery feed terminal should read ~12 V; control terminal should be low or open (not constant 12 V) until commanded
When commanded ON: one coil terminal ~12 V, the other should be pulled to near 0 V (ground) by the driver

Diagnostic algorithm

Read and record fault(s) and freeze frame. Clear codes and attempt to re‑create the fault to confirm repeatability.
Do a visual inspection of the rear wiper wiring, relay, socket, fuse, and connector for heat damage, corrosion, water entry, pin deformation, or chafing. Repair obvious damage.
Remove the wiper DOWN relay. Inspect relay terminals and relay socket for melted or bridged contacts. Replace relay if suspect.
Measure coil resistance across the relay coil terminals (relay removed). If resistance is very low (
With harness connected and ignition ON (engine off), backprobe the relay coil feed terminal and control terminal: verify battery feed (~12 V) and that the control side is not showing constant battery voltage when it should be inactive. If both terminals show battery, you have a short to battery on the control circuit.
If control circuit shows battery when it should be inactive, disconnect the rear wiper motor/module connector. If the code clears or the control circuit voltage changes, the short is downstream (toward motor/module). Inspect and repair that wiring or motor/module connector.
If disconnecting the motor does not change the fault, trace the control wire toward the BCM/ECU. Check for continuity to battery positive and inspect harness for chafing, pin contact with power feeds, or aftermarket taps.
If wiring appears intact and short persists, test the BCM/ECU driver output per OEM procedure. Replace BCM/ECU only after verifying wiring and relay are good and following manufacturer diagnostics.
After repairs, reinstall components, clear codes, and confirm by actuating the rear wiper through all functions and rechecking for DTCs.

Likely causes

Damaged/chafed wiring in harness causing constant 12 V on the relay coil control circuit
Failed relay with coil internally shorted to battery
Corroded/contaminated connector at relay socket or rear wiper motor connector
BCM/ECU output transistor failed closed (providing battery voltage)

Fault status

⚠️ Status

Rear wiper DOWN relay coil control circuit is shorted to battery voltage. Relay or wiring receiving constant 12 V where a switched/control signal is expected.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours