B16D3 – Right daytime running lamp fault – open circuit or short to positive (Mercedes-Benz)

B16D3 means the right daytime running lamp (DRL) on your Mercedes-Benz has an electrical fault. You will usually see the right DRL out, flickering, or behaving oddly. That changes how visible the vehicle looks in daylight. According to Mercedes-Benz factory diagnostic data, this code indicates a right DRL circuit fault that the module interprets as an open circuit or a short to positive. In plain terms, the vehicle tried to power the right DRL and did not see the electrical response it expected. The code does not prove the LED unit failed. It only identifies the suspect circuit path.

B16D3 Quick Answer

B16D3 points to the right DRL circuit on a Mercedes-Benz: the circuit looks open or shorted to battery positive. Start with the right front lamp connector, wiring damage, and water intrusion before replacing parts.

What Does B16D3 Mean?

Official definition: “Right daytime running lamp fault – open circuit or short to positive.” In practice, the right DRL may not illuminate, may flicker, or may stay brighter than commanded. The controlling module decided the right DRL output did not behave correctly when it commanded the DRL on or off.

What the module checks: the module monitors the right DRL output electrically, not visually. Depending on the Mercedes-Benz platform and lamp design, it may check output current draw, output voltage behavior, and plausibility between the command and the measured load response. Why it matters: an “open circuit” points you toward loss of continuity or high resistance, while a “short to positive” points you toward unwanted battery feed on the control wire. Both conditions can produce a dead lamp, but they require different tests before any parts decisions.

Theory of Operation

On Mercedes-Benz vehicles, the DRLs run through a body lighting control strategy. The control unit commands the right DRL on under defined conditions. It supplies power through a protected driver stage, and the lamp returns current through its ground path.

B16D3 sets when the module commands the right DRL and sees an electrical response outside its expected window. An open circuit usually comes from a broken wire, poor terminal fit, corrosion, or a failed internal lamp circuit. A short to positive happens when the output wire contacts a battery feed, or when a connector bridges terminals with moisture or melted plastic.

Symptoms

These symptoms fit a right DRL circuit fault on Mercedes-Benz vehicles.

• Right DRL out on the instrument cluster message or an obvious right-side DRL failure
• Flicker of the right DRL, especially over bumps or during engine vibration
• Intermittent operation where the right DRL works after a restart, then fails again
• Bright or stuck-on DRL if the circuit has an unintended positive feed
• Left DRL normal while only the right side shows a fault
• Repeated code reset where B16D3 returns quickly after clearing and re-testing
• Moisture clues such as fogging in the right lamp or water in the connector area

Common Causes

• Open circuit in the right DRL feed wire: A broken conductor stops current flow, so the body control output cannot drive the lamp and the module flags an open.
• Short to B+ on the right DRL control circuit: Contact with a battery-positive source forces the line high, so the module sees an implausible “always powered” condition.
• High resistance at the right headlamp/DRL connector: Corrosion or spread terminals add resistance, which drops voltage under load and makes the module interpret the circuit as open.
• Incorrect bulb or LED module fitted on the right side: The wrong load profile can trigger Mercedes-Benz lamp diagnostics, which then interprets the circuit state as open or short to positive.
• Water intrusion in the right lamp housing: Moisture bridges terminals and creates intermittent shorts to positive or unstable current draw during DRL operation.
• Harness damage near the right front corner: Chafing at brackets or radiator support areas can open the circuit or expose the conductor to a powered source.
• Fuse or power distribution fault for exterior lighting: A poor fuse contact or power distribution issue can remove supply or create a voltage condition that mimics an open circuit.
• Control module output driver fault (after circuit proof): An internal high-side driver can fail and stick high or stop switching, but you must confirm wiring integrity first.

Diagnosis Steps

You need a scan tool that can access Mercedes-Benz body/lighting data and run output tests. Use a quality DVOM, a test light that draws load, and back-probing tools. Have wiring diagrams and connector views for the Sprinter 907 lighting circuits. A headlamp access mirror and terminal tension tools help you catch spread pins.

1. Confirm DTC B16D3 and record freeze frame data. Focus on battery voltage, ignition state, exterior light switch state, DRL request status, and any companion lighting DTCs. Freeze frame shows the conditions when the fault set. Use a scan tool snapshot later to capture live data during a wiggle test or road test.
2. Do a fast visual inspection before any meter work. Check the right DRL for obvious damage, water in the lens, or signs of overheating. Inspect the harness routing at the right front corner for rubbing, pinch points, or recent collision repairs. Look for aftermarket splices, trailer wiring taps, and non-OE bulbs.
3. Check fuses and power distribution for the exterior lighting circuits. Verify each related fuse fits tight and shows no heat discoloration. Do not rely on continuity only. Load-test the fuse circuit with the lamp commanded ON, or use a test light from the fused output to ground.
4. Verify module power and grounds under load, not just with a static voltage reading. Command DRL ON and perform voltage-drop tests across the body module ground path while the circuit operates. Keep ground drop under 0.1 V with the load active. A high-resistance ground can create false open/short interpretations.
5. Use the scan tool to command the right DRL output ON and OFF, if the system allows it. Watch the status feedback for the right DRL circuit and compare it to the left side. If the command changes but the feedback stays “active” or “fault,” you likely have a wiring short to B+ or a driver issue.
6. At the right DRL connector, check for the correct power and ground behavior while commanding DRL ON. Use a test light to ground and to power as appropriate, so the circuit carries load. If the module drives a high-side output, you should see switched power at the control wire during activation. If power stays present when commanded OFF, suspect a short to B+ or a stuck driver.
7. Inspect and test the connector and terminals closely. Unplug the right lamp connector and look for green corrosion, moisture tracks, or overheated plastic. Check terminal tension with the proper gauge pin. Repair any pushed-back terminals. Poor pin fit often creates an “open circuit” only when vibration increases resistance.
8. Isolate the circuit to separate harness faults from lamp faults. Substitute a known-good load or a fused test light in place of the right DRL element. Command DRL ON and see if the module can drive the test load without immediately resetting B16D3. If the code does not return with the substitute load, the lamp assembly or internal lamp electronics likely caused the fault condition.
9. Check for a short to B+ with the connector unplugged. With ignition OFF, measure resistance between the DRL control wire and battery positive. Then repeat with ignition ON, because some circuits only show bias when powered. A hard short will show strong evidence in both states. If the reading changes with harness movement, you have chafing or water intrusion.
10. Perform a harness wiggle test while monitoring live data. Keep DRL commanded ON and watch the right DRL feedback status and voltage readings. Move the harness at the right headlamp pocket, along the radiator support, and at any inline connectors. Use a scan tool snapshot to capture the moment the signal drops or sticks high.
11. Clear codes and run a confirmation test. Cycle ignition, command DRL operation, and recheck for pending versus stored results. For lighting circuits monitored continuously, a hard fault usually returns immediately at key-on or when you command the output. If B16D3 stays cleared and the DRL operates correctly, the repair holds.

Professional tip: Treat “open circuit or short to positive” as two different electrical failures that can look similar on a quick check. A corroded connector can mimic an open under load, then recover with no load. Always test with the DRL commanded ON and use voltage-drop and a test light load. Compare right-side readings to the left side whenever access matches.

Possible Fixes

• Repair open or high-resistance wiring in the right DRL circuit: Repair broken conductors, chafing damage, or poor splices found during load testing and wiggle tests.
• Clean, dry, and restore terminal fit at the right lamp connector: Remove corrosion, correct pin tension, and repair water entry so the circuit carries current without voltage loss.
• Correct a short to B+ in the harness: Reroute and protect the harness, repair insulation damage, and remove improper aftermarket taps that backfeed battery voltage.
• Replace the right DRL lamp unit only after circuit proof: Replace the lamp assembly or DRL LED module if a known-good load test shows the wiring and module output operate correctly.
• Repair fuse/power distribution concerns: Replace heat-damaged fuse contacts or repair the affected power feed after you prove the loss under load.
• Control module output repair or replacement after verification: Address a failed output driver only after you confirm no short to B+ exists and the harness passes load and isolation tests.

Can I Still Drive With B16D3?

You can usually drive a Mercedes-Benz Sprinter 907 with B16D3, since the code targets the right daytime running lamp circuit. The van will not lose engine power from this fault. Still, treat it as a visibility and compliance problem. The right DRL may stay off, stay on, or act erratically. That changes how other drivers see you in daylight. In some regions, DRLs must work for inspection. If the lamp housing shows heat damage, melting, or a burning smell, stop driving until you verify the circuit. A short-to-positive can overheat wiring and connectors.

How Serious Is This Code?

B16D3 ranges from a nuisance to a real electrical risk. It stays mostly an inconvenience when the right DRL simply fails due to an open circuit, like a poor connector fit or a broken wire. It becomes more serious when the code sets for “short to positive.” In that case, the circuit may backfeed power, keep the lamp on, or stress the control output. Repeated overcurrent events can damage terminals, melt insulation, or affect nearby lighting circuits. Drivability typically stays normal, but safety can drop in poor weather or low-contrast daylight. Confirm the fault type with testing before any part replacement.

Common Misdiagnoses

Technicians often replace the right DRL lamp unit first, because the complaint looks obvious. That wastes time when the fault comes from an open in the harness near the headlamp, a connector pin spread, or corrosion at the front-end junction. Another common miss involves “short to positive.” People blame the module output, then skip a harness inspection. A pinched wire near the radiator support can feed voltage into the control line. Shops also misread a shared ground issue as a DRL failure. Avoid guesswork. Load-test power and ground, then verify the control line integrity under the same conditions that set the code.

Most Likely Fix

The most common confirmed repair direction involves the right front DRL circuit connection, not the lamp assembly. Focus on the headlamp connector, intermediate connectors, and harness routing at the right front corner. Clean and tension terminals, then repair any broken conductor or chafed insulation found during a wiggle test. For “short to positive,” find the backfeed source by isolating sections of the harness and checking for unwanted voltage on the control circuit with the lamp disconnected. After the repair, clear codes and verify operation through the DRL command or lighting status data. Drive conditions and enable criteria vary by 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