FAQ
TL;DR: VW Crafter/Sprinter cabin light faults often trace to the SAM output stage; this case showed 3 lamp wires and “the lamp works” on external 12 V. [Elektroda, wacek, post #16770458]
Why it matters: This FAQ helps Crafter 2.5 TDI owners diagnose no‑interior‑light issues without guesswork or unnecessary parts swaps.
Quick Facts
- Two codes observed: 9042 (front interior light implausible) and 90B5 (SAM output stage status implausible). [Elektroda, wacek, post #16770458]
- Front dome lamp wiring noted: +12 V constant, constant ground, and ground on door/remote trigger. [Elektroda, wacek, post #16761579]
- Cargo area darkness fixed by bulb replacement; cabin remained dark despite good fuses and lamp. [Elektroda, wacek, post #16761579]
- Swapping the SAM for repair/diagnosis is possible; proper coding of equipment may be required. [Elektroda, sk700, post #16770923]
- LED retrofits can trigger bulb‑out/short detection and set errors on this platform. [Elektroda, krzysiokal, post #16763515]
What do error codes 9042 and 90B5 mean on a VW Crafter 2.5 TDI?
9042 flags an implausible front interior light function. 90B5 reports the SAM (N10) output stage with an implausible status. Together they point to a control‑side fault, not necessarily the bulb. One owner translated these codes from the Sprinter 906 twin, which shares the SAM logic. [Elektroda, wacek, post #16770458]
How can I confirm the SAM module is the culprit for no cabin light?
Isolate the lamp feed at the SAM connector with the three related wires. Apply a stable external 12 V to the lamp circuit. If the dome light illuminates, the lamp and wiring are good, and the SAM output stage is suspect. As one tester noted, “the lamp works” when powered directly, indicating internal SAM failure. [Elektroda, wacek, post #16770458]
How do I check the interior light circuit with a multimeter?
Set the lamp switch to the constant‑on position. Measure for a short from the lamp feed to battery positive, not just continuity. If no short appears, substitute a known‑good lamp and retest. This separates wiring and load faults from SAM control faults during diagnosis. [Elektroda, sk700, post #16769788]
Can I just replace the SAM without coding?
You can swap the SAM to confirm damage. For a permanent replacement, plan to code the equipment so the new unit matches the vehicle configuration. This ensures all supervised loads and features behave correctly after installation. [Elektroda, sk700, post #16770923]
Do LED bulbs cause interior light errors on Crafter/Sprinter?
Yes. Low‑cost LEDs can trip the bulb‑out detection and mimic a short‑to‑positive condition. If LEDs are installed, refit a standard bulb or use CAN‑bus‑compatible LEDs with proper load. “You’ll always have errors” when detection is active and load is too low. [Elektroda, krzysiokal, post #16763515]
My cargo lights now work after bulb changes, but the cabin lamp stays dark. What next?
Verify fuses again, then focus on the cabin lamp control path. The user with this symptom had a good lamp and fuses, with three wires present. That narrowed the fault to the SAM‑controlled ground path for door/remote activation. Test at the SAM connector or substitute power to confirm. [Elektroda, wacek, post #16761579]
What wires feed the front dome lamp on this vehicle?
+12 V constant supply, a constant ground, and a switched ground that goes active with door opening or remote unlock. Knowing these helps you meter the circuit and separate supply issues from SAM‑controlled switching faults. [Elektroda, wacek, post #16761579]
Why does my light work with the button but not when I open the door?
Manual switch forces the lamp on, bypassing the door‑triggered ground path. If door‑open activation fails, suspect the SAM’s supervised output stage or its logic. Several owners report manual‑only lighting with door‑trigger failure. [Elektroda, pastylutza, post #19462408]
Is a short to positive likely here, and how do I verify it?
The scan shows a short‑to‑positive flag. Pull the lamp housing, visually inspect for chafing, and meter the feed while the switch is at constant light. Check fuses before and after testing. This approach verifies a genuine short versus a control‑stage interpretation. [Elektroda, krzysiokal, post #16740732]
Are the electric mirrors related to the interior light fault?
One report shows mirror adjustment working while the interior light automation failed. That suggests the mirror circuit is separate from the failing SAM output stage. Do not assume mirrors will fail with the dome light issue. [Elektroda, pawko122, post #17452431]
What is the SAM module on Crafter/Sprinter?
SAM is the Signal Acquisition and Actuation Module. It supervises loads like interior lights and reports implausible output states. In the Sprinter 906 twin, it’s referenced as unit N10, aligning with the error translations used for diagnosis. [Elektroda, wacek, post #16770458]
How do I rule out the lamp and wiring in three quick steps?
- Set the dome switch to constant light.
- Measure for shorts with a meter, not just continuity.
- Substitute a known‑good bulb and retest.
These steps isolate load and wiring before condemning the SAM. [Elektroda, sk700, post #16769788]
Could a high‑draw bulb mimic a short and trigger SAM protection?
Yes. An over‑current bulb or poor shunt sensing can look like a short. One advisor recommended replacing the bulb first to avoid misdiagnosis and possibly inspecting the current‑sense path in the SAM if replacing the module. [Elektroda, sk700, post #16770519]
What proportion of cases show module fault versus bulb/wiring?
In this thread, at least one case confirmed the lamp and wiring worked on external 12 V, pointing to the SAM output stage. Two distinct codes were logged. Treat the SAM as suspect after basic lamp and wiring tests. [Elektroda, wacek, post #16770458]
Why does the cluster show a yellow bulb warning after a while?
The SAM supervises circuits and flags a bulb‑out or implausible state on the dash. One owner saw the yellow lamp symbol despite manual lamp operation. That supports a monitored output not meeting expected current or state. [Elektroda, pawko122, post #17452431]
What unanswered question from the thread can we resolve? Can the SAM be replaced with matching numbers only?
You can install a same‑number SAM to test, but for a proper fix you should code it to the vehicle’s equipment. Coding aligns supervised outputs and avoids persistent warnings. [Elektroda, sk700, post #16770923]
