00979 – Right low beam headlamp bulb – open circuit/short circuit to B+ (Volkswagen)

Volkswagen-specific code — factory diagnostic data

Last updated: March 31, 2026

Definition source: Volkswagen factory description · Autel MaxiSys Ultra & EV. Diagnostic guidance is based on factory-defined fault logic for this code.

00979 means your Volkswagen has a fault in the right low beam headlamp circuit, so the right dipped beam may not work. In real driving, that reduces night visibility and can make the vehicle illegal to drive after dark. According to Volkswagen factory diagnostic data, this code indicates an open circuit or a short circuit to B+ (battery positive) on the right low beam headlamp bulb circuit. That wording matters because it points to wiring and power-feed behavior, not just a “bad bulb.” You must prove the circuit fault with basic electrical checks before you replace parts.

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00979 Quick Answer

The vehicle detects a problem in the right low beam bulb circuit: the circuit goes open or it gets fed battery positive when it should not. Expect the right low beam to be inoperative or behave abnormally until you repair the circuit issue.

What Does 00979 Mean?

Official definition: “Right low beam headlamp bulb – open circuit/short circuit to B+.” In plain terms, the control module sees the right low beam output as electrically wrong, so it cannot drive or monitor the bulb correctly. In practice, the right low beam often stays off, works intermittently, or triggers a lamp warning.

What the module checks and why it matters: On Volkswagen platforms, the body electrical controller (or related lighting controller) typically monitors the low-beam output stage and circuit load. It looks for expected current flow and expected voltage behavior when it commands the lamp on or off. An open circuit means the module commands the lamp but sees no usable load path. A short to B+ means the output or lamp feed shows battery positive at the wrong time, or it backfeeds the module. These two failure patterns require different tests, so you must confirm which condition you have before any repair.

Theory of Operation

Under normal operation, the Volkswagen lighting controller supplies power to the right low beam and completes the circuit path through the bulb and ground. Depending on the exact Caddy lighting design, the controller may switch the power side, the ground side, or use an internal electronic driver. The module also checks circuit integrity by monitoring current draw and output voltage.

This DTC sets when the controller commands the right low beam and the circuit feedback does not match the command. An open circuit happens when the filament fails, a connector loses contact, or a wire breaks. A short to B+ happens when the low-beam output wire contacts a constant battery feed, when water intrusion bridges terminals, or when an incorrect bulb or socket creates internal backfeed. The controller stores 00979 to identify the affected lamp circuit so you can test that branch, not guess at parts.

Symptoms

You usually notice this code as a right-side lighting complaint first, then a stored fault in the lighting electronics.

• Right low beam out on the passenger side (most common)
• Bulb warning or exterior lamp message on the cluster, if equipped
• Intermittent light that flickers with bumps or steering movement
• Abnormal behavior such as the lamp glowing when it should be off (backfeed/short to B+ pattern)
• Other lamps affected on the same housing if the connector overheats or melts
• Stored lighting fault in the body/central electronics module during a scan
• Heat smell near the headlamp area from a high-resistance connection

Common Causes

• Open filament or failed right low-beam bulb: A broken filament stops current flow, so the module sees an open circuit on the right low-beam output.
• Bulb connector heat damage or poor terminal tension: Loose or overheated terminals add resistance, which can mimic an open and trigger lamp-out monitoring.
• Harness damage near the right headlamp: Chafing or a pulled wire can open the circuit or rub through and contact a B+ feed.
• Short to B+ in the right low-beam control wire: Contact with a constant battery feed backfeeds the lamp circuit and sets a “short circuit to B+” type fault.
• Corrosion in the headlamp housing connector or splice: Corrosion raises resistance and can create unstable contact that the Volkswagen control module flags as a circuit fault.
• Incorrect bulb type or improper aftermarket HID/LED kit: Non-OE loads can confuse the lamp diagnostic, and some kits backfeed B+ into the control circuit.
• Fuse or power distribution fault feeding the headlamp circuit: A blown fuse, overheated fuse leg, or loose fuse carrier connection can create intermittent open-circuit behavior.
• Body Control Module (BCM/Central Electronics) output stage problem: An internal driver fault can stop current delivery or falsely detect a short, but you must prove the wiring first.

Diagnosis Steps

You need a scan tool that reads Volkswagen body faults and live data, a DVOM, and a test light. Use a fused jumper or a headlamp-load tool if available. Grab basic hand tools to access the right headlamp connector. Plan to perform voltage-drop tests under load, not just continuity checks.

1. Confirm DTC 00979 and record all stored and pending faults. Save freeze frame data if the module provides it. For this circuit code, focus on battery voltage, ignition state, light switch position, and any lamp-request status. Freeze frame shows conditions when the fault set. Use a scan tool snapshot later to capture an intermittent dropout during a wiggle test.
2. Inspect the full circuit path before meter work. Check the right low-beam bulb, connector seating, and any signs of melting. Look for harness chafing at the radiator support and behind the right headlamp. Verify no aftermarket HID/LED hardware ties into the low-beam wiring.
3. Check fuses and power distribution for the headlamp system. Do not go straight to the BCM connector. Inspect the fuse element and the fuse blades for heat discoloration. Load-test the suspect fuse circuit with the low-beam commanded ON. A fuse can look good and still fail under load.
4. Command the right low-beam ON with the switch and, if supported, with the scan tool output test. Observe whether the left low-beam works normally. A side-to-side comparison helps you spot a wiring or load issue fast.
5. Verify power and ground at the right low-beam bulb connector with the circuit loaded. Use a test light or the actual bulb as the load. Then perform voltage-drop testing on the ground side while the lamp should operate. Keep ground drop under 0.1 V with the circuit operating. A high-resistance ground can pass continuity checks and still fail in real use.
6. Check for “short to B+” behavior on the control or feed wire. Turn the low-beams OFF and key ON. Measure for unexpected battery voltage at the right low-beam terminal that should not have B+ at that moment on your Volkswagen wiring design. If you find backfeed, unplug the headlamp connector, then recheck. Next unplug any intermediate connectors to isolate where B+ enters the circuit.
7. Prove the circuit integrity between the bulb connector and the BCM/Central Electronics output. Keep the battery disconnected when doing resistance checks. Use an end-to-end continuity test, then follow with a loaded test using a fused jumper and a test light. Continuity alone cannot find a high-resistance splice or a strand-broken wire.
8. Inspect and test the connectors that carry the right low-beam circuit. Pay attention to terminal spread, water entry, and green corrosion. Perform a pin-drag test if you have the tools. Wiggle-test the harness while monitoring scan tool lamp status or voltage at the bulb. Use a scan tool snapshot to capture the moment the voltage drops during the wiggle.
9. If wiring and load test good, verify BCM power and grounds under load before condemning the module. Perform voltage-drop tests at the BCM ground pins while the lighting load operates. A weak BCM ground can create false “open/short” lamp diagnostics. Fix power or ground issues before any module decisions.
10. Clear codes and run the same conditions that set the fault. Cycle the ignition and command low-beam ON several times. A hard fault on a continuously monitored lamp circuit often returns immediately at key-on. If it stays cleared, complete a road test at night conditions if safe. Re-scan to confirm no pending or stored return.

Professional tip: Treat the FTB subtype as your direction finder. “Short to Battery (B+)” means you must hunt for backfeed or a rubbed-through control wire. “Open circuit” means you must prove load, connector tension, and voltage drop under real current. The DTC text names the suspect area, not the failed part.

Possible Fixes

• Repair the right low-beam bulb connection: Clean corrosion, restore terminal tension, and replace a heat-damaged connector pigtail only after you verify voltage drop problems.
• Repair harness damage or a short to B+: Re-insulate or replace damaged wiring, then secure the harness to prevent future chafing near the right headlamp.
• Correct fuse or power distribution issues: Replace an overheated fuse, repair loose fuse carrier terminals, and restore proper feed to the lighting circuit.
• Install the correct bulb and remove backfeeding aftermarket equipment: Fit the proper Volkswagen-specified bulb type and eliminate HID/LED wiring that injects battery voltage into the control circuit.
• Restore ground integrity: Clean and tighten the affected ground point and confirm less than 0.1 V drop with the lamp commanded ON.
• Address a verified BCM output fault: Replace or repair the BCM only after you prove correct inputs, solid powers/grounds, and a failed output driver under load.

Can I Still Drive With 00979?

You can usually drive a 2013 Volkswagen Caddy with DTC 00979, but you should treat it as a lighting safety fault. This code points to the right low beam circuit showing an open circuit or a short to battery positive (B+). If the right low beam stays off, you lose forward lighting coverage and visibility on that side. If the circuit shorts to B+, the lamp may stay on unexpectedly. That can drain the battery and create heat at a damaged connector. Avoid night driving or poor weather driving until you confirm proper low beam operation. If fuses blow repeatedly, stop driving and diagnose the circuit.

How Serious Is This Code?

00979 ranges from an inconvenience to a real safety issue. It stays minor if the lamp works normally and the code sets only intermittently. It becomes serious when the right low beam does not light, flickers, or causes repeated fuse failures. Lighting faults raise crash risk at night and reduce your vehicle’s conspicuity. A short to B+ can also keep the lamp on with the key off. That can discharge the battery and overheat a poor connection. This code does not affect engine drivability, but it affects road legality and safety. Fix it before extended driving in darkness.

Common Misdiagnoses

Technicians often replace the right low beam bulb immediately and stop there. That wastes time when the real fault sits in the connector, ground, or harness near the headlamp housing. Another common mistake involves blaming the body control module without proving the output driver misbehaves. Always confirm the circuit state at the headlamp connector first. Shops also miss fitment issues after bulb replacement. A partially seated bulb or spread terminal can mimic an open circuit. For “short to B+” subtypes, many skip a proper short test and overlook aftermarket wiring or moisture inside the headlamp. Prove the fault with voltage, load, and continuity checks.

Most Likely Fix

The most frequently confirmed repairs involve the right low beam bulb connection and wiring, not the control module. Start by verifying the bulb seats correctly and the terminals grip the bulb pins tightly. Then inspect the right headlamp connector for heat damage, corrosion, or water intrusion. If the code indicates a “short to battery (B+)” subtype, isolate the harness and locate where the low beam feed contacts a constant B+ source. If it indicates “open circuit,” perform a voltage drop and continuity test between the control module output and the lamp. Clear the code and confirm the low beam operates through several key cycles and a short road test, since enable criteria vary by Volkswagen platform.

Repair Costs

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