P38A Bulb Failure message preconditions?

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ar1g3

ar1g3

Well-Known Member
Posts
148
Location
Belgium
Hi all,

I am trying to find out how the BECM determines if a bulb has blown. What are the parameters it looks at?

I have a trailer and each time I use it I get the error 'RH Tail Light Bulb Failure' and it shuts off all RH tail lights. Which is super annoying. Also there is no blown bulb..
When I connect the trailer to another vehicle there's no issue. No issue when no trailer connected either. Just renewed the socket and plug on trailer and car.

Maybe if I know how the BECM detects bulb failure I can find out why it give false alarms.

Anybody any clue?
 
It probably measures the current, and alerts if it's too low or open circuit. It might also check for excessive current or short, but RAVE only mentions bulb failure detection. Tail, Brake & Fog lamp share same output for car & trailer.

For indicators the rear & trailer are fed from different output, so BECM lights up the trailer indicator in the dash.

See Section P1 in RAVE !!

1718980544341.png
1718980556917.png
 
pwood999 said:
It probably measures the current, and alerts if it's too low or open circuit. It might also check for excessive current or short, but RAVE only mentions bulb failure detection. Tail, Brake & Fog lamp share same output for car & trailer.

For indicators the rear & trailer are fed from different output, so BECM lights up the trailer indicator in the dash.

See Section P1 in RAVE !!

View attachment 319801View attachment 319802
Click to expand...
As above. Sounds to me as if the trailer lights have been spliced into the rear lights rather than using the connectors that are there for the trailer.
 
Thanks everyone!

The trailer does not have led lights and from what I could see it's an original tow hitch with original wiring.

I was thinking that too high current would be the problem as I have double side marker lights on the trailer. Both are spliced into the corresponding's trailer rear light. And then there's also the numberplate lights.

But it seemed weird that it would detect too high current as a blown bulb.
 
ar1g3 said:
Thanks everyone!

The trailer does not have led lights and from what I could see it's an original tow hitch with original wiring.

I was thinking that too high current would be the problem as I have double side marker lights on the trailer. Both are spliced into the corresponding's trailer rear light. And then there's also the numberplate lights.

But it seemed weird that it would detect too high current as a blown bulb.
Click to expand...
No Load or overload are both fault conditions.
 
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