B3801 – Passenger Compartment Lamp Request Circuit

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

Definition source: SAE J2012 naming/structure guidance

What Does B3801 Mean?

B3801 – Passenger Compartment Lamp Request Circuit is an ISO/SAE controlled Body system diagnostic trouble code that indicates a circuit fault in the electrical path used to request passenger compartment (interior) lamp operation. In other words, the module responsible for monitoring the interior lamp request signal is detecting an electrical circuit condition that is not within the expected range or behavior for that request input.

This code is focused on the request circuit (the input signal and its wiring/connectors), not on the lamp bulbs themselves. A B3801 setting means the control module cannot reliably interpret the interior lamp request because of an electrical circuit problem such as an open, short, or high resistance in the request signal path.

Quick Reference

• DTC: B3801
• Official Title: B3801 – Passenger Compartment Lamp Request Circuit
• System: Body
• Standard classification: ISO/SAE Controlled
• Fault Type: Circuit
• What it indicates: The passenger compartment lamp request input circuit is not being read correctly due to an electrical fault in the circuit.
• Likely affected functions: Interior/courtesy/dome lamp request behavior (turn-on, turn-off, delay/dimming functions where applicable).

Symptoms

When B3801 is present, symptoms typically involve interior lighting that does not respond correctly to a request, responds at the wrong time, or behaves inconsistently.

• Interior lamps do not turn on when requested: For example, opening a door or using the interior lamp switch may not trigger the passenger compartment lamps.
• Interior lamps stay on: Lamps may remain illuminated after the request should end, potentially leading to battery discharge.
• Intermittent interior lamp operation: The lighting request may work sometimes and fail other times due to an unstable circuit connection.
• Incorrect response to request inputs: Lighting behavior may not match the request state being commanded by switches/inputs.
• Battery drain: If the circuit fault results in lamps staying on or the vehicle not entering a low-power state.

Common Causes

B3801 is a circuit fault code, so causes generally involve electrical integrity issues in the passenger compartment lamp request circuit (signal wiring, terminals, and related connections).

• Open circuit in the passenger compartment lamp request wiring (broken conductor, damaged harness)
• Short to ground on the request circuit
• Short to voltage on the request circuit
• High resistance in the request circuit (partially broken wire, corrosion at terminals, poor pin fit)
• Connector or terminal damage (loose, backed-out, spread, corroded terminals; moisture intrusion)
• Fault in the request input device that creates an invalid electrical signal for the circuit (for example, a switch/contact that does not produce the expected electrical state)
• Power or ground issue affecting the module’s ability to correctly read the request input circuit (verify relevant fuses/feeds/grounds per wiring diagram)

Diagnosis Steps

Diagnosis should focus on verifying the request circuit’s electrical behavior and determining whether the fault is an open, short, or high resistance condition. Use a scan tool that can access Body codes and data, a digital multimeter, and the correct wiring diagram for the exact vehicle configuration.

1. Confirm B3801 and record data: Scan for B3801 in the Body system, note status (current/history), and record any available freeze frame/failure records.
2. Check for additional related codes: If other Body or communication codes are present, address them as directed by service information because they may affect how the request circuit is interpreted.
3. Verify the symptom: Operate the interior lamp request inputs (interior lamp switch positions and any request triggers applicable to the vehicle design) and observe whether the passenger compartment lamps respond correctly.
4. Monitor the request input in scan tool data: Locate the data parameter that corresponds to the passenger compartment lamp request (naming varies by vehicle). Toggle the request and confirm the input changes state cleanly and consistently. If it does not, continue with circuit testing.
5. Perform a visual inspection of the circuit: Inspect accessible portions of the request circuit harness and connectors for abrasion, pinched wiring, broken insulation, moisture, or terminal damage.
6. Check module power and ground integrity: Using the wiring diagram, verify that the controlling module’s power feeds and grounds are correct under load. An unstable power/ground can cause inaccurate circuit interpretation.
7. Test the request circuit voltage/state at the module: Back-probe the module input (as specified by the wiring diagram) and measure how the signal behaves when the request is commanded on and off. Compare readings to service information expectations.
8. Check for open/high resistance: With power off as required by service procedures, perform continuity testing end-to-end on the request circuit and measure resistance. High resistance or intermittent continuity indicates wiring or terminal issues.
9. Check for shorts: With the circuit isolated as needed, test for unintended continuity between the request circuit and ground or voltage sources. A short can hold the request line in an incorrect state.
10. Isolate the fault location: If readings change during gentle harness movement, focus on that section and inspect for internal wire breaks or terminal fit problems.
11. Test the request input device: If the circuit checks good, test the input device according to the wiring diagram (expected open/closed states, reference voltage behavior, or resistance values as applicable).
12. Clear and recheck: After repairs, clear DTCs and repeat the same request operations that previously caused the code. Confirm normal lamp request behavior and that B3801 does not return.

Possible Fixes

Fixes depend on what testing confirms. Address circuit integrity first before considering module replacement.

• Repair an open/high resistance in the passenger compartment lamp request circuit (repair/replace damaged wiring, correct poor splices, restore proper terminal contact)
• Repair a short to ground or short to voltage in the request circuit (locate chafed insulation or pinched harness and restore proper routing/protection)
• Clean, repair, or replace connectors/terminals with corrosion, moisture intrusion, or poor pin fit
• Repair power/ground issues that affect the module’s ability to read the request circuit correctly (fuses, feeds, ground points as specified by service information)
• Replace the request input device if it fails circuit-level testing and produces an incorrect electrical output
• Replace the controlling module only after testing verifies correct power/ground and a known-good request circuit signal reaching the module input

Can I Still Drive With B3801?

In many cases, the vehicle remains drivable because B3801 is a Body system code related to the Passenger Compartment Lamp Request Circuit, not a powertrain or braking function. However, the impact can still matter:

• Practical concern: Reduced or incorrect interior lighting can affect visibility inside the passenger compartment.
• Electrical concern: If the circuit fault causes lamps to remain on, the battery may discharge while parked.

If the interior lamps do not time out or remain illuminated when the vehicle is off, addressing the fault promptly helps prevent a no-start condition due to a discharged battery.

Repair Costs

Repair cost depends on whether the confirmed root cause is wiring, connector condition, a switch or module issue, or the labor needed to diagnose the fault correctly.