B1391 — Oil Level Switch Circuit Failure

Will B1391 clear itself?

Sometimes B1391 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.

What are the symptoms of B1391?

Drivers most often notice: warning light on the dashboard, the affected function (locks, windows, lighting, wipers) works intermittently or not at all, no impact on engine operation in most cases.

Is it safe to drive with B1391?

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 much does it cost to fix B1391?

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

What is the most common cause of B1391?

The most common causes are: corroded or loose connectors, faulty switch, motor or actuator of the affected system, blown fuse or failed relay.

When the powertrain control module or body control module detects an abnormal electrical condition in the oil level detection circuit, it logs trouble code B1391. This fault falls under the body electrical category and specifically points to an oil level switch circuit failure. In plain terms, the module is reporting that the signal coming from the oil level sensor does not match what it should see under normal operating conditions.

Unlike some codes that trigger on a single reading, B1391 typically requires the fault to appear repeatedly under specific circumstances before the check engine light illuminates. This is why the freeze frame data saved alongside the code is so valuable—it records engine load, RPM, coolant temperature, and vehicle speed at the exact moment the problem was detected. You can use this snapshot to recreate the conditions that caused the failure when you begin testing.

The affected system here is straightforward: the oil level switch monitors engine oil quantity and sends that information to the control module. When the circuit experiences resistance, opens, or shorts unexpectedly, the module logs B1391 and flags the fault. Depending on your vehicle's design, this may also trigger a dashboard warning or affect other body functions that share the same circuit.

Common Symptoms of B1391

• The check engine light or dedicated warning indicator illuminates on the dashboard
• The specific function tied to the oil level circuit operates intermittently or stops working entirely
• In most cases, engine performance and drivability remain unaffected
• Some vehicles may display an inaccurate oil level reading on the driver information center
• The oil pressure warning light could accompany the code on certain makes

What Causes B1391

The root cause of B1391 is usually found in the wiring or connections before the control module itself:

• Corroded, oxidized, or loose electrical connectors in the oil level sensor circuit
• Wiring damage where harnesses pass through door jambs, firewalls, or areas exposed to moisture
• A defective oil level switch or associated actuator motor
• Blown fuse or failed relay feeding the affected circuit
• Body control module internal fault, though this is less common
• Water intrusion into connectors, particularly in vehicles frequently exposed to rain or car washes

How to Diagnose B1391

Follow these steps methodically to isolate the failure point:

1. Connect an OBD2 scanner and confirm B1391 is present in the stored codes. Record the freeze frame data—it reveals exactly what engine conditions coincided with the fault detection.
2. Pull all related codes from the module. Secondary codes often point to the actual root cause rather than the symptom code. Cross-reference manufacturer technical service bulletins for your specific make and model, as factory-issued updates may address recurring B1391 issues.
3. Perform a thorough visual inspection of the wiring harness feeding the oil level switch. Look for cracked insulation, bare wire, corrosion buildup, and any signs of previous repairs that may have failed.
4. Access the live data stream and monitor the oil level sensor PID while operating the ignition in the conditions specified by the freeze frame. The signal should respond predictably as you cycle the key.
5. Examine connectors at flex points—areas where wiring bends repeatedly such as door hinges and tailgate openings. These stress points fracture internally before showing external damage.
6. Clear the code, complete a full drive cycle that reproduces the freeze frame conditions, and verify B1391 does not reappear. If it returns, you have narrowed the problem to the circuit you tested.

Repair Options and Costs

Address the most accessible and likely culprits before committing to expensive replacements:

• Replace faulty oil level switch or actuator: parts and labor $120–$450 depending on vehicle accessibility
• Body control module diagnosis, repair, or replacement: $300–$900 depending on whether the module can be repaired or requires new hardware
• Wiring harness repair or connector replacement: $80–$250 for most scenarios

Total Repair Cost for B1391

B1391 repair typically ranges from $80 to $900 depending entirely on which component is responsible. The majority of cases involve damaged wiring or a faulty switch, falling in the lower to mid range. Control module replacement represents the maximum scenario but occurs far less frequently. Spending time on accurate diagnosis before purchasing parts prevents wasted money on components that are not actually faulty.

Can You Drive with B1391?

B1391 is generally considered safe to drive short distances—the oil level circuit does not directly control engine operation or safety-critical systems. However, if the fault affects exterior lighting, windshield wipers, or central locking, address these promptly. Driving with inoperable wipers in poor weather or unsecured door locks presents genuine safety concerns that justify sooner rather than later repair.

Related OBD2 Codes

• B1300: Power Door Lock Circuit Failure
• B1301: Power Door Lock Circuit Open
• B1302: Accessory Delay Relay Coil Circuit Failure
• B1303: Accessory Delay Relay Coil Circuit Open
• B1304: Accessory Delay Relay Coil Circuit Short To Battery
• B1305: Accessory Delay Relay Coil Circuit Short To Ground