B1838

Code

Other B — Body

Battery Saver Power Relay Circuit Failure

Brand: Other

Type: B — Body

Views: UK: 24 EN: 40 RU: 26

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Page language: EN

Causes

Faulty Battery Saver (power) relay
Blown fuse protecting relay or circuit
Wiring fault: open, short to ground or short to B+ in relay circuit
Corroded/loose relay socket or connector pins
Weak or discharged battery / poor battery connections
Body Control Module (BCM) / Powertrain Control Module (PCM) internal driver fault or software anomaly

Symptoms

Interior accessories remain powered or do not switch off as expected after key‑off
Battery drain when vehicle is parked (battery discharging)
No click from the battery saver relay when expected
Intermittent accessory function (dome lights, radio memory loss)
Associated warning lights or additional body electrical codes
Vehicle may fail to enter sleep mode or have parasitic drain

What to check

Read and record freeze frame / stored DTCs with a scan tool; note any related body or powertrain codes
Check battery state of charge and health; ensure battery terminals are clean and tight
Visually inspect fuses and relay for corrosion, melting, or blown condition
Listen for relay click with ignition/key cycles or when commanded from scan tool
Inspect relay socket and wiring harness for heat damage, corrosion, or pin damage
Perform a wiggle/test while monitoring circuit voltage to look for intermittent faults

Signal parameters

Battery voltage at rest: ~12.0–12.8 V (12.6 V nominal fully charged)
Charging/engine running: ~13.5–14.8 V
Relay coil resistance (typical): 50–200 ohms (vehicle-specific; compare to known-good or service spec)
Control signal to relay coil: switched ground or +12 V depending on design; expect near 0 V or battery voltage when not energized and ~12 V (or grounded) when commanded
Switched output (relay common to load): near battery voltage when relay closed, open/near 0 V when open
Parasitic draw (with vehicle asleep): normally

Diagnostic algorithm

Verify DTC and related codes with a scan tool; record freeze frame. Clear codes and attempt to re-create.
Check battery condition and terminals; charge or replace if low. Retest with fully charged battery.
Visually inspect the relay and fuse for the battery saver circuit. Replace suspect fuse/relay with known-good part and re-scan.
Locate relay pins: identify coil and contact circuits. With connector disconnected, measure coil resistance and compare to spec.
With scan tool or manual command, energize the relay while monitoring the coil control line for the expected control voltage (or ground). If control signal is present but relay does not operate, replace relay.
If relay operates but loads behave incorrectly, measure voltage at relay common (battery feed) and at switched output with relay both energized and de‑energized to confirm switching action.
Inspect harness: perform continuity tests from relay socket to BCM/ground/load; check for short to ground or B+ on output or control wires using a multimeter/bench power where appropriate.
Wiggle test wiring/connectors while monitoring circuit to find intermittent faults; repair broken wires or corroded terminals.
If wiring and relay are confirmed good but control signal is missing or abnormal, inspect BCM power/grounds and communication lines. Check for other BCM codes (U-codes) and test BCM outputs per service manual.
After repairs, clear codes and perform battery drain test/overnight soak to confirm no parasitic draw and verify DTC does not return.
If BCM is suspected faulty after exhaustive wiring/relay checks, follow manufacturer procedure for BCM bench testing, reprogramming, or replacement.