B3138 – All Door Lock Circuit High (BCM)

System: Body | Standard: ISO/SAE Controlled | Fault type: Circuit High

Definition source: SAE J2012/J2012DA (industry standard)

B3138 – B3138 – All Door Lock Circuit High (BCM)

B3138 means the body control module (BCM) has detected the “all door lock” control circuit is reading higher than expected (a circuit-high condition). In real-world terms, the power lock system may behave unpredictably: doors may not lock when commanded, may lock by themselves, or the BCM may disable the function to protect the circuit. This is a body (non-powertrain) fault, so it typically won’t affect drivability, but it can create a security and safety issue if the vehicle won’t lock reliably. Because “circuit high” often points to a short to power, poor ground, or an open circuit, verifying the exact wiring and lock-control strategy for your model is critical.

The B3138 code indicates the BCM is seeing an abnormally high voltage on the all-door-lock control circuit, commonly caused by a short to power, an open ground/return path, or a wiring/connector fault that keeps the circuit “high,” leading to lock operation failures or erratic behavior.

What Does B3138 Mean?

B3138 is a standardized body diagnostic code that, by definition, points to an “all door lock circuit” high-voltage condition detected by the BCM. The BCM monitors the electrical state of the lock command circuit(s) it uses to request locking for all doors. When the circuit voltage stays above the expected threshold (or behaves as if it is being held high) outside normal command conditions, the BCM flags B3138. The exact circuit design can vary by make/model/year (for example, low-side driver vs. high-side driver logic), so confirm the circuit behavior with a wiring diagram and voltage testing at the BCM and door lock control paths.

Theory of Operation

Under normal operation, the BCM interprets lock requests from switches, key fob/remote receiver inputs, or network messages, then drives the all-door lock control circuit using an internal driver. Depending on the design, the BCM may apply battery voltage (high-side control) or provide a ground path (low-side control) to energize relays/actuators or to signal a door module. The circuit state should transition cleanly between “rest” and “command” states.

A “circuit high” fault means the BCM is detecting voltage on the monitored lock control circuit that is higher than the expected value for the current operating state. Common electrical explanations include a short to battery voltage on the control wire, an open in the ground/return path that prevents the circuit from pulling low when commanded, or a connector/terminal issue causing unintended voltage presence. Because the BCM both commands and monitors the circuit, the fault can set when the circuit is stuck high, intermittently spikes high, or does not change as expected during commanded lock events.

Symptoms

• Power locks inoperative: pressing the lock switch or remote may not lock all doors consistently.
• Intermittent locking: doors may lock only sometimes, especially after bumps, door movement, or temperature changes.
• Uncommanded locking: the vehicle may lock unexpectedly if the circuit is being held high or shorted to power.
• Locks only from one input: locks may work from the key fob but not from the interior switch (or vice versa), depending on circuit routing.
• Security/entry warnings: body-related warnings or chimes may occur if the BCM detects abnormal lock control behavior.
• Battery drain (sometimes): a circuit held “active” can keep modules awake or energize related components, depending on design.

Common Causes

• Cause: Short to power on the all-door lock control circuit (chafed harness contacting B+), forcing the BCM input/output to read high
• Cause: Open ground on the door lock switch/module side, creating a “pulled-up” high voltage condition at the BCM due to loss of return path
• Cause: Open or high-resistance in the all-door lock control circuit (broken wire, partially backed-out terminal) causing the BCM to see an abnormally high signal
• Cause: Corroded, water-intruded, or loose connector/terminal at the BCM or door lock circuit junction, increasing resistance and distorting the voltage level high
• Cause: Door lock switch assembly or related input device internally shorted to power, holding the circuit high when it should toggle
• Cause: Aftermarket alarm/remote start/keyless entry splice backfeeding voltage into the lock circuit, elevating the circuit above expected levels
• Cause: Damaged door-jamb harness (flex point between body and door) with intermittent short-to-power or open ground when the door moves
• Cause: Body Control Module (BCM) internal driver/input fault or internal pull-up malfunction (rare; confirm only after circuit tests pass)

Diagnosis Steps

Use a capable scan tool that can access Body/BCM codes and data, a digital multimeter (preferably with min/max capture), and the correct wiring diagram for your exact vehicle. A test light and back-probing pins help confirm power/ground without damaging terminals. If available, an oscilloscope can quickly spot a stuck-high control line or backfeed.

1. Verify B3138 is current: scan the BCM for stored and pending codes, record freeze-frame or failure records (when it set, voltage state, command state), and check for other body/DTCs that may point to shared power/ground or network concerns.
2. Confirm the complaint: operate lock/unlock from the driver switch, passenger switch (if equipped), key fob, and any interior lock button. Note if locks are inoperative, stuck locked/unlocked, cycle by themselves, or work intermittently.
3. Perform a quick visual inspection of likely failure points: door-jamb rubber boots, harness bends, recent repairs, and any non-factory splices for alarms/remote start. Look for pinched wires, rubbed insulation, or moisture intrusion.
4. Check BCM powers and grounds first: with key on, verify the BCM’s main feeds and grounds meet spec on the wiring diagram (low voltage drop on grounds). A weak ground can make multiple BCM circuits read incorrectly high.
5. Identify the exact “all door lock” circuit at the BCM connector using the wiring diagram. Back-probe the circuit and measure voltage with the system at rest (no lock/unlock request). Compare to expected behavior for that design (many circuits toggle between near-0V and near-B+ or use a pulled-up logic voltage).
6. Command the locks with a scan tool output test (if supported) while monitoring the circuit voltage. If the voltage remains high regardless of command, suspect a short to power/backfeed or an open ground/return path depending on the circuit design.
7. Isolate the backfeed: disconnect related door lock switches/modules (one at a time if multiple) and recheck the circuit voltage at the BCM. If the “stuck high” condition drops to normal after unplugging a component, that branch/component is suspect.
8. Check for short to power: with the circuit disconnected at both ends when possible, measure resistance from the circuit to B+ and inspect for continuity that should not be present. Wiggle the door-jamb harness while watching the meter to catch intermittent faults.
9. Check continuity and voltage drop end-to-end: perform a continuity test from BCM pin to the next connector/component pin, then perform a loaded voltage drop test (where applicable) to reveal high-resistance terminals that continuity alone can miss.
10. Inspect terminals closely: look for spread terminals, corrosion, partially backed-out pins, and water trails at the BCM connector and door connectors. Repair terminal fitment issues and retest before condemning any module.
11. If all wiring/components test good and the circuit behavior at the BCM remains abnormally high, follow service information to confirm BCM internal fault (for example, compare the measured pin state to commanded state and to a known-good reference circuit). Only then consider BCM repair/replacement and required programming.

Professional tip: A “circuit high” code like B3138 is frequently caused by a short-to-power or a lost ground that makes the line float high—so always prove the circuit can be pulled low under load (and that it isn’t being backfed by aftermarket accessories) before replacing a BCM or switch.

Possible Fixes

• Repair chafed wiring or insulation damage causing a short to power in the all-door lock control circuit
• Restore ground integrity (clean/tighten ground points, repair open ground wire, correct high voltage drop)
• Clean, dry, and secure BCM/door connectors; repair or replace corroded terminals and ensure proper pin tension
• Remove or correct aftermarket alarm/remote start/keyless entry wiring that is backfeeding the lock circuit
• Replace a faulty door lock switch/input device that is holding the circuit high (only after isolation testing confirms it)
• Repair damaged door-jamb harness sections and add proper strain relief to prevent repeat failures
• Reprogram/replace the BCM if internal failure is confirmed by pin-level testing and all external circuits are verified good

Can I Still Drive With B3138?

Usually yes, because B3138 is a body-system fault where the BCM is seeing the all-door-lock control circuit stuck high (higher than expected voltage). It typically won’t affect engine performance, but it can affect safety and security: doors may not lock/unlock reliably, locks may cycle unexpectedly, and you could be unable to secure the vehicle. If the locks behave erratically while driving (unexpected locking/unlocking) or you cannot lock the doors at all, limit driving and repair soon. If the issue is accompanied by battery drain, overheating at a switch/connector, or repeated fuse issues, stop driving and diagnose immediately to prevent electrical damage.

How Serious Is This Code?

B3138 is generally a medium-severity diagnostic code because it impacts a critical convenience and security function (power door locks) and can create secondary problems like a parasitic draw if the circuit is being held high continuously. The “circuit high” fault type points to a short to power, high-voltage feedback, or an open/failed ground path in the lock control circuit, so ignoring it can lead to intermittent lock operation, BCM stress, blown fuses, or connector/terminal overheating. While it usually won’t strand you mechanically, it can leave the vehicle unsecured or create an electrical reliability issue that worsens over time.

Repair Costs

Last updated: March 21, 2026