355 Convertible Top Control Module Repair

Was he talking about the driver’s seat not moving forward?

I’d still check the passenger pot resistance at the ECU. These things can break at any time. The pot ball and socket may not be gripping, depending on temperature and humidity.

 

Dan - could it be simply that both seats or either seat is not all the way back, fully away from the dash and steering column?

I'm trying to recall, but I seem to remember on my 355 if the passenger seat was positioned where it was not in the way of the top operation - in other words, if the seat wasn't all the way back, then it would not move when I operated the top. My wife always sat closer to the dash than I did to the steering wheel, so her seat (passenger side) was never in the way of the top operation and mine always was, so my (driver's) seat always moved forward when operating the top open/close switch.

 

@DanRC30 I don’t see your point about the PO’s comments. Didn’t you find some dodgy wiring on the driver’s side which you repaired? See Feb 17th.

Apart from driver’s seat movement limitations, the drivers’ seat operates normally. Why are you now suspecting an ECU fault? You haven’t checked the passenger pot yet.

 

You've said that you suspected the Roof ECU twice, and seemed to be leaning away from the passenger seat pot being faulty. I just wanted you to check the pot before you went looking at Roof ECU repair. If you're opening or closing the roof and the Roof ECU thinks the passenger seat is fully forward because of faulty pot (even though the seat isn't actually fully forward), it will shut off power to the seat motor and not move the seat forward at all.

Simplified check: If you move the seat fully back with the seat switch and check the pot reading at the ECU and it reads high resistance between pins B-18 and D-16*, and low resistance between B-18 and B-16, you'll know that the pot is faulty.

*also at D-5 and D-7 (because these are jumpered to D-16)

Of course, for a full check of the pot, you'd probably need to measure the resistance at both ends of seat travel and perhaps at the mid point.

 

Yes. Don't test the ECU pins, test the sockets on the ECU plugs (car side)

The sockets are shown in this diagram:

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B-18 has a black/blue wire.
B-16 has a grey/yellow wire.
B-16 has a black wire/s.

 

I would do the pot resistance checks as follows:

1. Move both seats fully back
2. Disconnect the plug from the roof controller
3. Measure the resistance ground to pin B-18 (passenger's seat) and ground to pin X-?? (equivalent pin for the driver's seat)

If you don't get similar resistances for the two, it would mean one of the pots is out of adjustment.

If you get very big difference between the two (like closer to zero on one and closer to max on the other), the possibility is that yellow and black wires have been swapped-over on one of the pot connectors.

 

B-19

 

The last line in your post #209 - I believe you mean "D-16" (the black ground wire).

 

Ah, correct. Typo.

 

Both seem high, especially B-18 passenger seat. Maybe you need to run the seats fully forward and re-measure.

I'm not saying my values are correct, but here's what I got previously:

Passenger (fully aft): 924 ohms (B-18)

Passenger (fully fwd: 4329 ohms (B-18)

Driver (fully aft) : 576 ohms (B-19)

Driver (fully fwd) : 3742 ohms (B-19)

After your fully forward, repeat the fully aft measurement to see if the values are consistent.

My values were recorded directly at the potentiometers, but there shouldn't be too much difference at the ECU

I've seen one aft value on the forum which was slightly above 1000 ohms.

 

If possible, both ways. That way we can establish what is the possible range and what is the actual range.

 

I'm wondering if driving a seat to its mechanical limits will keep resetting the pot (thanks to the slip of the ball and socket). If you drive it all the way forward, will this make the seat not go back far enough (because the electronic SD1-tool limits set at the factory are limiting the range)?

I forgot to ask my tech how the SD1 tool works.

 

Just asked my tech about the SD1 calibration...

It doesn't involve disconnecting the pots. You just run the seats forwards and backwards. Then the SD1 tool tells you to move the seats into a green zone (on the display).

This still doesn't make sense to me. It doesn't explain how to move the seats fully forward and fully back (as in your situation)... unless the SD-1 tool temporarily overrides the potentiometer's effect on seat movement.

 

Something definitely strange going on here:

1) Driver seat value changing, but range seems limited. Did the seat actually move further with the pot disconnected?

2) Passenger seat value not changing.

I’m assuming the diagrams are correct (regarding pin numbers). Did you confirm pin numbers with the assistance of wire colours?

I would first think that:

1) the driver’s pot was positioned in the wrong position during installation. Is it possible to partially remove the seat with the seat fully aft on the rails (pot connector disconnected), then remove the case from the pot and try to adjust the potentiometer independently of seat movement so that the potentiometer reads 500~1000 ohms. Then reinstall. Or did you try this already and couldn't get enough forward movement (perhaps because of the ECU programming). Note that the seat pots seem to be non-linear, so adjusting them at the lower end of resistance may show a big difference at the forward end.... kilo ohms instead of a few ohms.

2) the passenger seat pot has broken. The ball and socket may not be gripping.

The forward values are all the same (and somewhat atypical). I suppose the seat pots may have been disturbed in the past.

 

That was a typo... See Miro's correction. Resistance checks were meant to be between B-18/B-19 and D-16, but any good ground should replace D-16..... Although, testing with D-16 also checks the ground wire between the pot and the Roof ECU.

 

ah, I see what you mean. I have resistance values for D-16 (from my car), but I have to convert them from my pot wire colours to pin numbers.

Another thought.... I'm slightly concerned that the ECU pin resistance readings may not be the same as direct pot readings because of shared wiring between the passenger and driver's seat. With the passenger seat forward or aft and your new driver's pot plug disconnected, can you retake the passenger measurement across B-18 and D-18 and see if the value is different?


Regarding my pot values (using pot wire colours)

e.g. the red pot wire on my car corresponds to the black wire (D-16)

Passenger (fully aft)
red-black = >4kohms
red-yellow = 924ohms
yellow-black = 3940ohms

Passenger (fully fwd)
red-black = >4kohms
red-yellow = 4329ohms
yellow-black = 543ohms

Driver (fully aft)
red-black = >4kohms
red-yellow = 576ohms
yellow-black = 4218ohms

Driver (fully fwd)
red-black = >4kohms
red-yellow = 3742ohms
yellow-black = 1028ohms

My ohmmeter is only designed for low resistances, so I don't get a reading above about 4.4k ohms.

B-16 (grey/yellow) = yellow pot wire on my car.
D-16 (black - ground) = red pot wire on my car
B-18 (blue/black) = yellow passenger pot wire on my car (middle wire)
B-19 (grey/blue) = yellow driver pot wire on my car (middle wire)