B162A – Left low beam fault – open circuit or short to positive (Mercedes-Benz)

B162A means your Mercedes-Benz has detected a problem in the left low beam circuit, so the left headlight may not work. You will notice reduced night visibility and a higher safety risk first. According to Mercedes-Benz factory diagnostic data, this code indicates a left low beam fault caused by an open circuit or a short to positive. In plain terms, the control module tried to command the left low beam on or monitor it, but the electrical results did not match what it expects. This is a manufacturer-specific code, so Mercedes-Benz logic and wiring design determine the exact test method and monitoring strategy.

B162A Quick Answer

B162A on Mercedes-Benz points to the left low beam circuit having an open circuit or a short to battery positive. Diagnose the wiring, connectors, bulb/LED driver, and control output before replacing parts.

What Does B162A Mean?

Official definition: “Left low beam fault – open circuit or short to positive.” In practice, the vehicle cannot reliably power or control the left low beam. The result ranges from a dead left low beam to a lamp that behaves inconsistently. The code does not prove a bad bulb or lamp unit. It flags the circuit as the suspected trouble area.

What the module checks: the body lighting controller monitors the left low beam command and the circuit’s electrical response. Depending on Mercedes-Benz platform design, it may watch output current, output voltage feedback, or a dedicated sense line. Why that matters: an open circuit can look like “no load,” while a short to positive makes the circuit appear powered when it should not. Those two failure types lead you down different test paths, so you must confirm the circuit state with measurements under load.

Theory of Operation

Under normal conditions, a Mercedes-Benz body/lighting control module commands the left low beam on and regulates power to the lamp circuit. The module expects a predictable electrical load and feedback when the lamp operates. The system may also use bulb-out monitoring to protect wiring and report lamp failures to the cluster.

B162A sets when the module commands the left low beam and sees an implausible circuit condition. An open circuit removes the expected load, so current draw falls outside the expected window. A short to positive backfeeds battery voltage into the circuit, so the module “sees” power when it should not. Either condition can also trigger protective shut-down of the output driver.

Symptoms

Drivers and technicians usually notice one or more of these symptoms with B162A:

• Left low beam out on the driver’s side, especially at night
• Warning message for exterior lighting or low beam malfunction in the cluster
• Intermittent operation where the left low beam works after cycling the switch
• One-sided lighting pattern with reduced roadway illumination on the left
• Headlamp flicker on the left low beam (more common with poor connections)
• Related lighting codes stored for left headlamp supply or monitoring, depending on equipment
• Output protection where the module disables the left low beam after repeated faults

Common Causes

• Left low beam bulb or LED module open internally: An internal open stops current flow, so the body lighting driver sees an open circuit on the left low beam output.
• Harness open between the front lamp and the lighting control output: A broken conductor or pulled terminal interrupts the load path and triggers the “open circuit” portion of the fault.
• Short to positive on the left low beam control line: Chafing to a B+ feed backfeeds the output, so the module sees voltage present when it commands the lamp off.
• Corrosion or heat damage at the left headlamp connector: Added resistance reduces current and distorts feedback, which can look like an open circuit to the monitoring strategy.
• Incorrect bulb type or aftermarket lamp assembly: The wrong load profile changes current draw and feedback behavior, so the module flags a circuit fault even if the lamp illuminates.
• Water intrusion inside the left headlamp housing: Moisture creates leakage paths and intermittent shorts, often presenting as a short-to-positive or unstable output state.
• Fuse, power distribution, or splice issue feeding the headlamp circuit: A compromised feed can remove power under load and make the module interpret the circuit as open.
• Output driver protection event inside the lighting control module: A previous short can trip protection logic, leaving the channel disabled and appearing as an open circuit until the root cause is removed.

Diagnosis Steps

You need a scan tool that can access Mercedes-Benz body/lighting data, plus a DVOM and a test light. Use back-probing pins and a wiring diagram for the left low beam circuit. A headlamp load tool or known-good bulb helps confirm current capability. Plan for voltage-drop tests under load, not continuity alone.

1. Confirm DTC B162A and record freeze frame data. Focus on battery voltage, ignition state, exterior lighting switch position, and any lamp command status. Note whether the code shows as pending versus stored, since a hard circuit fault often returns immediately on key-on.
2. Perform a fast visual inspection of the left low beam circuit path before meter work. Check the left headlamp for water, melted connectors, and pin fit. Inspect the harness where it bends near the lamp, radiator support, and any recent repair area.
3. Check fuses and power distribution that feed the left headlamp and the lighting control channel. Verify the fuse holds under load, not just visually. If the platform uses a fused distribution block or splice pack, inspect for heat discoloration and loose terminals.
4. Verify module power and grounds under load using voltage-drop testing. Turn the low beams on, then measure ground drop at the module ground path while the circuit operates. Keep ground drop below 0.1V with the circuit loaded, since a weak ground can mimic an open circuit.
5. Use the scan tool to command the left low beam on and off, if supported. Watch live data for left low beam request, output status, and any “short to B+ / open load” flags. If the scan tool supports it, capture a manual snapshot during a wiggle test to catch intermittent changes.
6. Check whether the left low beam illuminates and compare brightness to the right side. If the lamp works but B162A sets, suspect a load mismatch, incorrect bulb, or feedback anomaly. If the lamp stays off, continue with circuit testing.
7. At the left headlamp connector, test for proper feed and control behavior while the lamp is commanded on. Use a test light or load tool to confirm the circuit can deliver current. Do not rely on an unloaded DVOM reading, since high resistance can still show “normal” voltage.
8. Test for an open circuit by loading the circuit and measuring voltage drop across the suspect section. Measure from the module output pin to the headlamp connector pin while commanded on. A large drop points to resistance in wiring, splices, or terminals between those points.
9. Test for a short to positive on the low beam control line. With the lamp commanded off, check whether the control/output line still shows B+ behavior relative to ground. If it does, isolate by disconnecting the headlamp and then rechecking to determine whether the short sits in the lamp assembly or the vehicle harness.
10. Inspect connector terminals closely and correct any mechanical causes. Look for spread terminals, backed-out pins, green corrosion, or heat-tinted plating. Perform a pin drag test and repair terminal tension issues, since intermittent opens often set this DTC during vibration.
11. After repairs, clear codes and run a verification test. Cycle the lighting commands and perform a short road test with a wiggle test in safe areas. Confirm the left low beam operates and B162A does not return as pending or stored.

Professional tip: Use freeze frame to decide if you chase an “open” or a “short to positive” first. An open usually sets when the module commands the lamp on and sees no load response. A short-to-positive often sets when the module commands the lamp off and still sees voltage on the output. That logic saves time and prevents unnecessary lamp or module replacement.

Possible Fixes

• Repair open in the left low beam wiring: Restore continuity and current capacity at the damaged section, then verify with a loaded voltage-drop test.
• Repair short to positive in the harness or lamp assembly: Isolate the shorted branch, correct chafing or internal lamp faults, and confirm the output no longer backfeeds with the lamp commanded off.
• Clean and restore terminal integrity at the headlamp connector: Remove corrosion, repair overheated terminals, and ensure proper pin tension to prevent intermittent opens.
• Install the correct Mercedes-Benz-specified bulb or approved lamp assembly: Correct the load profile and connector fit issues, then confirm the monitoring no longer flags a fault.
• Restore power distribution integrity: Replace a compromised fuse, repair a loose fuse block terminal, or repair a damaged splice that drops voltage under load.
• Re-enable and verify the lighting output after root-cause repair: If the module latched protection, clear DTCs and retest outputs, then confirm the driver operates normally.

Can I Still Drive With B162A?

You can usually drive a Mercedes-Benz Sprinter with B162A, but you should treat it as a lighting safety issue. This code points to the left low beam circuit showing an open circuit or a short to positive. If the left low beam does not work, night driving becomes risky and may be illegal. If the circuit shorts to positive, the lamp may behave erratically, create warning messages, or trigger protective shutdown inside the lighting control electronics. Drive only in good daylight until you confirm proper low beam operation. If you smell burning insulation, see smoke, or repeatedly blow a fuse, stop driving and diagnose the circuit immediately.

How Serious Is This Code?

B162A ranges from an inconvenience to a serious safety concern. It feels minor when the low beam still works and the code sets intermittently from a loose connector. It becomes urgent when the left low beam stays off, since you lose forward lighting and visibility. A “short to positive” condition can also stress wiring and connectors. Mercedes-Benz lighting modules may disable an output to protect the circuit, which can leave you with no headlamp on that side. The code does not usually affect engine drivability, but it directly affects nighttime safety and your ability to be seen.

Common Misdiagnoses

Technicians often replace the bulb or headlamp assembly first because the symptom looks obvious. That wastes time when the real fault sits in the connector, harness, or a damaged ground path. Another common mistake involves ignoring the “short to positive” half of the definition. An open circuit and a short to B+ require different tests. Some also skip load testing and rely on a quick voltage check, which misses high resistance under load. Finally, clearing the code without checking live data and output control can hide an intermittent wiring fault until the next night drive.

Most Likely Fix

The most frequently confirmed repair directions for B162A involve restoring circuit integrity at the left low beam: cleaning and tightening the bulb or headlamp connector, repairing a rubbed-through harness section near the headlamp area, or correcting a poor ground that forces the circuit to backfeed. Do not treat these as certain. Verify the fault type first with scan-tool output testing and electrical checks at the lamp connector. After repairs, command the left low beam on and confirm stable operation through a road test, since enable criteria and lamp monitoring logic vary by Mercedes-Benz platform.

Repair Costs

Repair cost depends on whether the confirmed root cause is a sensor, wiring, connector issue, or control module problem. Verify the fault electrically before replacing parts.

Last updated: March 30, 2026