B137A

Code

Generic B — Body

Accessory Power Relay Control Circuit Malfunction

Brand: Generic

Type: B — Body

Views: UK: 17 EN: 23 RU: 20

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or short in relay control wiring (broken conductor, chafing to ground or battery)
Failed accessory power relay (stuck, coil open/short)
Corroded or loose connector at relay, fuse block, or module
Faulty ground or high-resistance ground connection
Blown or intermittent fuse supplying relay coil or module
Body control module (BCM) / powertrain control module (PCM) driver fault or software issue

Symptoms

Accessory circuits (radio, power outlets, cigarette lighter, etc.) fail to operate or operate intermittently
Accessory power only works in certain key positions or not at all
Fuses for accessory circuits may blow repeatedly
Possible parasitic battery drain if relay stuck closed
Diagnostic trouble code stored and possibly warning lamp/message depending on vehicle

What to check

Check stored freeze frame and readiness data with a capable scan tool
Visual inspection of relay, relay socket, fuse block and associated harness for corrosion, heat damage or water ingress
Verify battery voltage at rest and with ignition/accessory on (battery should be ~12.2–14.8 V when running)
Inspect and test related fuses and fusible links for continuity
Wiggle test harness while observing relay operation or DTC presence to find intermittent faults
Substitute a known-good relay of identical type and re-test

Signal parameters

Battery supply to relay/fuse block: ~12.2–14.8 V (engine running or charging)
Relay control output (module commanded OFF): ~0 V or open (depends on vehicle architecture)
Relay control output (module commanded ON): ~12 V or switched to ground depending on design (verify with service data)
Relay coil resistance (typical): tens to a few hundred ohms (refer to vehicle spec) — open circuit indicates failed coil
Contact continuity when relay energized: near 0 Ω between switched contacts; open when de-energized
Control circuit short threshold: a direct short to battery/ground will show near 0 Ω; open shows infinite Ω

Diagnostic algorithm

Retrieve DTC details and freeze-frame data with a scan tool; note key/ignition position and conditions when code set.
Visually inspect relay, relay socket, fuse block and wiring for damage, corrosion, or fluid intrusion. Repair any obvious issues.
Verify battery voltage and charge state. Replace or charge battery if voltage is low.
With ignition OFF, disconnect connector to accessory relay. Check coil resistance across relay coil terminals; compare to spec. If coil open or shorted, replace relay.
With relay installed (or substituted with known-good), command relay on/off using scan tool (if available) while measuring voltage at the relay control pin. Confirm the module is commanding expected voltage (ON vs OFF).
If the module commands correctly but relay does not operate, check supply fuse and supply voltage at relay coil positive terminal while commanded ON. Repair supply or replace relay.
If control output is stuck or shows unexpected voltage, measure continuity from module output to relay socket for short to battery or ground and for opens. Repair wiring as needed.
Check module ground(s) for low resistance to battery negative. Clean/tighten grounds if high resistance found.
If wiring and relay check good but fault persists, perform module-level diagnostics: check for related CAN communication DTCs, update/reflash module software per OEM service info, or consider module replacement only after wiring and components proven good.
After repairs, clear codes and perform operational test cycles to confirm the fault does not return and accessories operate normally.