B1691 — Autolamp Delay Circuit Short To Battery

OBD2 code B1691 flags a problem with the body electrical system (autolamp delay circuit short to battery). The car is usually drivable while you plan the repair. Common culprits: body control module (BCM) fault, blown fuse or failed relay, corroded or loose connectors.

body electrical

Is it safe to drive?

Short-term driving is OK Usually safe to drive — body codes rarely affect drivability. Exceptions: exterior lighting and wipers in bad weather, and central locking faults that can leave the car unsecured.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm B1691 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many B0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the body electrical system for damage, corrosion, chafing or poor contact.
Subsystem check Operate the affected function while watching its switch and motor PIDs in live data.
Subsystem check Inspect connectors and wiring at flex points (door jambs, tailgate hinges) — wires break there first.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm B1691 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for B1691 (parts and labor, USD, independent shop rates): BCM repair or replacement: $300–$900; Repair wiring or connectors: $80–$250; Replace the switch or actuator: $120–$450. Overall, fixing B1691 usually costs between $80 and $900. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What is the most common cause of B1691?

The most common causes are: body control module (BCM) fault, blown fuse or failed relay, corroded or loose connectors.

How much does it cost to fix B1691?

BCM repair or replacement — $300–$900; Repair wiring or connectors — $80–$250; Replace the switch or actuator — $120–$450. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Will B1691 clear itself?

Sometimes B1691 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

Is it safe to drive with B1691?

Usually safe to drive — body codes rarely affect drivability. Exceptions: exterior lighting and wipers in bad weather, and central locking faults that can leave the car unsecured.

What does OBD2 code B1691 mean?

When the engine control module detects that the autolamp delay circuit is feeding battery voltage where it should not, it logs trouble code B1691. This particular circuit controls the "on" time of your headlights after you turn off the ignition—a convenience feature that lights your path when you exit at night. The BCM (body control module) is the central hub managing this and dozens of other comfort and safety functions throughout your vehicle's body electrical system.

B1691 falls within the B-series codes, which cover body network faults across most manufacturers. When the BCM sees voltage levels that don't match what the autolamp delay circuit should produce, it flags the reading as abnormal and sets B1691 after the condition persists for a defined number of drive cycles. The module saves freeze frame data alongside the code, capturing engine RPM, load, coolant temperature, and vehicle speed at the exact moment the fault first appeared—information that proves invaluable when narrowing down the root cause.

The dashboard warning light is usually the first sign that B1691 has been stored. Beyond that, the autolamp function itself may behave erratically or stop working entirely. You might also notice issues with other body systems—windows, door locks, wipers, or exterior lighting—depending on whether the underlying fault is localized to a single circuit or points to a failing BCM. In most cases, engine performance and drivability remain completely unaffected.

Common Symptoms of B1691

Check engine or warning light illuminated on the instrument cluster
Autolamp delay feature not working or cutting out unexpectedly
Headlights staying on longer than programmed or not activating at all
Intermittent or complete loss of other body electrical functions (windows, locks, wipers)
No change to engine idle, acceleration, or transmission behavior
The affected function may work sporadically—working fine one moment, failing the next

What Causes B1691?

Damaged wiring ranks at the top of the list. The wires running through door jambs and tailgate hinges flex thousands of times over a vehicle's life, and the insulation eventually cracks. Once moisture and road salt get inside, corrosion eats away at the conductors and creates short circuits.

Loose or corroded electrical connectors produce the same symptoms. If the connector feeding the autolamp delay circuit is not making solid contact, resistance spikes can trick the BCM into thinking there's a short.

The body control module itself can fail, though this is less common than wiring issues. When the BCM's internal circuitry degrades, it may report phantom faults across multiple systems simultaneously.

A blown fuse or failed relay feeding the body electrical system will trigger B1691 if the autolamp circuit loses its ground reference or receives unexpected voltage.

A faulty switch—whether the headlight stalk, a door switch, or the delay timer module—can send incorrect signals that the BCM interprets as a short condition.

Worn motors or actuators in the affected lighting circuit occasionally draw too much current, causing voltage irregularities that the module flags as B1691.

How to Diagnose B1691

Start by connecting an OBD2 scanner and confirming that B1691 is stored in the BCM, not just the engine control module. Save the freeze frame data—this snapshot of engine conditions at the time of failure tells you whether the fault occurred at idle, highway speed, or during a cold start, which guides where to look first.

Check for any other body-related codes alongside B1691. Multiple codes pointing to the same area often indicate a shared wiring problem rather than separate component failures. Look up technical service bulletins for your specific make, model, and model year—manufacturers publish TSBs for many B0xxx code patterns, and some have documented factory fixes or software updates that a scan tool can apply.

Perform a thorough visual inspection of the wiring harness serving the autolamp circuit. Focus on areas where wires flex: door jambs, the tailgate opening, and behind the headlight assemblies. Look for chafed insulation, broken strands inside the wire, and any signs of moisture intrusion or corrosion on the pins inside connectors.

Use your scan tool's data display to monitor the autolamp circuit while operating the headlight switch through its full range. A lab scope or graphing multimeter connected to the circuit will reveal voltage spikes, drops, or erratic readings that indicate an intermittent short.

Inspect connectors at both ends of the circuit. Pull them apart, check for bent pins, corrosion buildup, and loose terminals. Apply electrical contact cleaner if you find corrosion, then reconnect and reseat everything firmly.

After clearing B1691, drive the vehicle through a complete drive cycle that recreates the conditions recorded in the freeze frame data. If the code returns, the fault is confirmed and active. If it stays cleared, you may have fixed an intermittent issue.

Repair Options for B1691

Wiring and connector repair is the most frequent fix. Depending on whether you need a simple splice, a new connector, or replacement of a damaged section, expect to pay between $80 and $250 for parts and labor at an independent shop.

If the body control module is diagnosed as the culprit, replacement or rebuilding typically runs $300 to $900. Remanufactured BCMs are available for many vehicles at the lower end of that range, while dealer-sourced new units push toward the higher end.

Replacing a failed switch, motor, or actuator in the autolamp circuit generally costs $120 to $450, depending on the component and labor access. The headlight switch stalk is often the offender and is usually on the cheaper side to replace.

How Much Does It Cost to Fix B1691?

The total depends entirely on what actually failed. Here is a breakdown of typical parts-and-labor costs at an independent repair shop:

BCM repair or replacement: $300–$900
Wiring or connector repair: $80–$250
Switch or actuator replacement: $120–$450

Most B1691 repairs land somewhere between $80 and $900. The single most important step is an accurate diagnosis before you buy any parts—the most expensive scenario is rarely where you should start.

Driving Safety Verdict

In most vehicles, B1691 does not compromise safe operation of the engine, transmission, or brakes. You can continue driving with the code present, but keep two things in mind: if the fault affects exterior lighting, you lose valuable visibility and have reduced presence for other drivers, which becomes a serious hazard in rain, fog, or darkness. A central locking fault that intermittently leaves the doors unlocked presents a security risk. Beyond those exceptions, B1691 is primarily a comfort and convenience issue rather than a drivability concern.