FAQ
TL;DR: On a 2003 Opel Vivaro 1.9, loss of indicators/hazards/horn/central light often traces to the cabin fuse feed from MAXI fuses—"one 70A and four 60A"—so verify power to the first fuse row and the UCH first. [Elektroda, mechelek, post #16938802]
Why it matters: This FAQ helps DIYers quickly restore dead cabin circuits and avoid immobilizer pitfalls after a UCH swap on Vivaro/Trafic/Primastar vans.
- Reported symptom cluster: indicators, horn, hazards, central locking, and interior light all dead while engine still starts. [Elektroda, mechelek, post #16938086]
- Vehicle in case study sat ~1 month with the battery removed before issues appeared. [Elektroda, mechelek, post #16938086]
- Engine can start and drive even when those body functions are down. [Elektroda, mechelek, post #16938682]
- Under‑bonnet supply noted as 1×70A + 4×60A MAXI fuses feeding cabin board. [Elektroda, mechelek, post #16938802]
- Swapping UCH may restore functions but immobilizer will block starting unless data is migrated. [Elektroda, mechelek, post #16951004]
Quick Facts
- Main battery fuse and engine‑bay fuses can test OK while the first cabin fuse row has no voltage; trace that feed. [Elektroda, mechelek, post #16938772]
- Replacing the UCH revived indicators, hazards, horn, and interior light in the case discussed. [Elektroda, mechelek, post #16951004]
- Immobilizer pairing lives in EEPROM (e.g., 93C66); moving data enables starts after UCH replacement. [Elektroda, piotrekwoj1, post #16951577]
- A “shock sensor” is not the fix when the engine already starts; focus on power feeds/UCH. [Elektroda, piotrekwoj1, post #19676405]
- Requesting wiring paths: power to UCH and to the first cabin fuse row were the key diagrams sought. [Elektroda, mechelek, post #16938974]
How do I diagnose no voltage on the first row of cabin fuses?
Confirm battery health, then probe both sides of each fuse in row one with ignition on. Back‑trace from under‑bonnet MAXI fuses to the cabin block. Verify continuity and feed to the UCH. If upstream fuses are live but the cabin rail is dead, suspect the UCH or its supply connector. Document readings and wiggle‑test harness sections between bay and cabin. This mirrors the thread’s initial finding of a dead first row despite good engine‑bay fuses. [Elektroda, mechelek, post #16938086]
What is the UCH on a Vivaro?
UCH is the body control module that distributes power and logic for indicators, hazards, horn, interior lighting, and central locking. Loss of its feed or internal failure can kill those circuits while the engine still runs. The original poster sought diagrams for UCH power paths, underscoring its central role in cabin electrics. [Elektroda, mechelek, post #16938974]
Could the engine still start if indicators, horn, and hazards are dead?
Yes. In the discussed case the van started, drove, and only body functions were down. That points to a body/control feed issue rather than engine management. This separation helps you avoid chasing ECU or fuel faults when the symptom set is purely cabin systems. [Elektroda, mechelek, post #16938682]
Which high‑current fuses feed the cabin board on this model?
The user confirmed an under‑bonnet set of MAXI fuses: one 70A and four 60A. These supply downstream cabin circuits, including the first fuse row. Inspect for voltage presence, not just continuity, and load‑test if necessary. “One 70A and four 60A” was noted during troubleshooting. [Elektroda, mechelek, post #16938802]
Is the main battery fuse the likely culprit here?
It can fail, but in the thread the main battery fuse and engine‑bay fuses tested OK while the first cabin row had no voltage. That steers diagnosis toward the UCH feed or the harness segment between the bay and the cabin fusebox. [Elektroda, mechelek, post #16938772]
What immediate fix restored the dead cabin functions in the thread?
Swapping in another UCH brought back indicators, hazards, horn, and interior lighting. This confirmed the original UCH or its data as the root cause for dead cabin circuits, though a start‑inhibit then appeared due to immobilizer pairing. [Elektroda, mechelek, post #16951004]
Why didn’t the van start after installing a replacement UCH?
The immobilizer data in the UCH didn’t match the vehicle. After replacement, the van’s body functions returned but the immobilizer blocked starting until data was migrated or paired. This is a typical outcome after a control unit swap without key/EEPROM transfer. [Elektroda, mechelek, post #16951004]
How do I make a replacement UCH start the van?
Move the immobilizer data. The forum guidance: reprogram or re‑solder the 93C66 EEPROM from the old UCH to the new one. As the expert put it, “Disconnection, no reprogramming,” meaning don’t try to bypass IMMO—transfer data correctly. [Elektroda, piotrekwoj1, post #16951577]
Could a shock or crash sensor cause these symptoms?
No, not when the engine starts. A respondent noted the car started, so focus on UCH supply and cabin feed rather than crash/shock sensors. Chasing those will waste time if the power rail to the cabin fuses is the real issue. [Elektroda, piotrekwoj1, post #19676405]
What’s a quick 3‑step check to isolate the fault?
- Verify live voltage at each MAXI fuse (70A/60A) under the bonnet.
- Probe both blades of each fuse in the first cabin row for 12V.
- If cabin row is dead but MAXIs are live, inspect UCH feed connector and swap‑test UCH (mind immobilizer). [Elektroda, mechelek, post #16938802]
Does leaving the van without a battery trigger these issues?
In the case discussed, the van sat about a month without a battery before symptoms were noticed. That context suggests corrosion, memory loss, or UCH stress might manifest afterward. Use it as a clue during history taking. [Elektroda, mechelek, post #16938086]
How should I test relays correctly when chasing body power faults?
Bench‑energize with 12V across coil terminals (e.g., 85/86) and confirm switched continuity on 30–87 under load. The OP used this method to verify ticking and output. Always load‑test; a relay can click yet fail under current. [Elektroda, mechelek, post #16938345]
What if all MAXI fuses are live but the first cabin row is still dead?
Then the failure lies in the feed path or UCH. Check the harness from engine bay to cabin, connector corrosion, and UCH internal faults. The thread’s turning point was acknowledging live MAXIs yet a dead cabin row, leading to UCH action. [Elektroda, mechelek, post #16938802]
What is a CAN bus?
CAN bus is the two‑wire network that lets modules like the UCH and ECU communicate. A dead power feed can mimic CAN faults by silencing modules. Restore clean power first, then investigate communications if symptoms persist. [Elektroda, mechelek, post #16938974]
Any edge cases to watch out for after a UCH swap?
A start block from immobilizer mismatch is normal after swapping UCHs. Until you migrate 93C66 data, the engine won’t crank or run despite restored body functions. Plan EEPROM work before concluding the repair. [Elektroda, mechelek, post #16951004]
Which wiring info should I request or print before testing?
Get the feed diagram from battery/MAXI to cabin fuse row and the UCH power/ground pinout. Those two views guided the original poster’s next steps and will accelerate your tracing. [Elektroda, mechelek, post #16938974]
