martinss

I mentioned my issue in a related thread, but so as not to hijack that thread here are my travails.

Car is a 1990 S4 euro. The headlight motor fails to stop on raising the headlights until the lift arm strikes the A/C condenser (to prevent further damage I placed a board against the condenser while testing). To do this, it over-rotates and starts to descend on the other side. The headlights come on, but are now pointing back somewhat.

I have read up on various posts, and understand that S4s have a motor that is driven in alternate directions through a roughly half circle arc, rather then running in a full circles to raise and lower, as was the case with earlier cars. They also do not have a diode in the motor to burn out. The motor arm can strike the wider condenser instead of the radiator if it is not stopped in time, as mine was. In earlier cars it strikes the radiator.

To begin my testing I disconnected the lift arm from the motor to the light bar. If I then turned on the lights (ignition on, switch in the headlight-on position) the motor ran, but did not stop. The headlights flashed on and off as the gearbox passed through the 'up' position. Turning off the headlights reversed the motor, which then came to a stop after some rotation (i.e. detected 'down').

The symptoms suggested that the disc and wiper arrangement in the motor gearbox that detects position was dirty and that the full 'up' position was not being detected, but the 'down' was. I therefore dismantled and cleaned. But on reassembly the symptoms persisted. The confusing factor here is that the headlights were apparently getting a signal that they had been raised and so came on transiently, but this same signal was not triggering the motor to stop.

The next obvious candidate was the double-sized relay. I have an '88 with functioning headlights. I swapped relays after confirming that they were exactly the same part number. The problem persisted.

So then I thought perhaps there was a motor fault. So I put the '88 motor in the '90 and got the same problem. I put the '90 motor in the '88 and it worked fine.

Just to be sure, I put both the good relay and motor in the '90 at the same time, but the problem persisted.

So, I have to conclude that the position signal for fully raised is being generated, but only acted on by the lights, not the motor, and that this is external to either the motor or the relay - presumably a wiring fault.

I will have to study the wiring diagram, but am hoping that someone on this forum has seen this before and could point me to a solution before I go cross-eyed studying the diagram.

Thanks.

Alan

The wiring diagram probably won't help you that much. This scheme for the pod motor control is 2 relay standard reversing drive.

Here below is a generalized schematic of how it works.

Note that some early S4+ HL relays don't have the control feature from X bus for the down control - on these the pods only stay up while the marker lights are on, on later cars if you turn the ignition off -> then the lights: the pods will stay up with the lights off.


The bottom line is that to have the symptoms you describe - you pretty much have to have a short to ground somewhere on the 56S wire connection. An open circuit here wouldn't allow the motor to run at all.

You can test for this first - remove the motor connector & remove the relay and test either the relay pin 56S or the car side of the motor connector on pin 3.

Alan

martinss

Thanks Alan. I removed the relay and disconnected the motor plug. Using a continuity meter connected to ground, I was not able to detect a return connection to ground by touching pin 3 on the car side of the motor plug, either with ignition and light switch off, or both on.

However, I did notice that the orange front sidelights do not light whether the light switch is set to sidelight or headlight, although the tail lights come on. Being a euro it does not have side markers. The driving lights do come on - I have DRLs.

On my '88 both the front sidelight and front-side orange marker lights come on.

I have a 2011 invoice from the PO for repair of headlight and sidelight wiring, so it is a recurring issue... No details of what they did though

Alan

Well I don't see how that could cause this - but it may give some clues as to what was changed.

What happens with motor disconnected, relay installed - lights on (position 2 - headlights).

Measure voltage between car side headlight motor connector pins 1 & 5 ?

0v difference or +- ~12v?

If +-12v the motor is being driven even without any limit switches connected... should not be... need to know why...


With HL motor connected and relay out - test relay pin 56s and see if it is grounded with the motor parked down - it should be - and should go OC when you wind it to the top (fully-up) position.

Alan

martinss

OK - In the first test there is 0v between 1 and 5, whether or not the ignition is off or on, or the light switch is in any position with the ignition on.

In the second test 56s is grounded on 'down' and open on 'up' (I ran the motor on my '88 to ensure it was up).

Thanks for all your help Alan.

Alan

OK here is a thought based on another post today...

I assume since this is a Canada car that you have DRL's? if so pull the DRL relay and see what happens?

Alan

jeff spahn

I have a spare DRL relay if you are in need of one. I'd let it go for a bit less than I paid for it to help you out.

Alan

Jeff - test your DRL relay as I noted in the other thread...

I think you and Martin may be suffering from the same failure - the diode in the relay seems to be SC (or not even there? - are these new DRL relays perhaps from the same source?) - would explain some symptoms.

The DRL's come on when the fuel pump turns on (engine is running) (on the 86 coil terminal) - except if the pods are up (implying you have HL instead) this via the diode to ground on the 85 terminal coil - so it is grounded only when the 56S connection from the motor is grounded (pods are down). In that case you can still turn them on with the foglight switch.

Now if the diode conducts both ways things work oddly when the fuel pump isn't running - the unpowered fuel pump motor low resistance to ground - grounds the coil and this feeds through the SC diode (in reverse) and grounds the 56S line to the relay (not very strongly - but enough). Now the HL relay thinks the pod never gets to the top...

This only occurs when the fuel pump isn't on (car off, accessory & ignition - but not yet started).

It will be maybe about 80-120 ohms - low enough.

I think it should work OK with the car running - verify?

Alan

FredR

It's no wonder people have night mares about 928 electrical problems!

Sounds as though someone outsmarted himself when designing the wiring circuits for these things.

Fred

jeff spahn

Works perfectly with ignition running. Exhibits symptoms when ignition not running.

Alan

Well lets see what Martin has to say.

Fred - the wiring is actually fine, Porsche does lots of interesting interlocks between systems - they work fine as long as all the component work - when they don't it gets interesting to debug. These days thats true of most cars - though car technicians now just swap out all the offending stuff for a fix.

In this case and for many other things it would be generally better if the diode were separate and the relays mostly all generic types. Too many special cases that are becoming NLA/expensive even though they are really quite simple things.

Alan

martinss

Yeah - RESOLUTION

Sorry to be slow responding. After work today I pulled the DRL relay and the lights worked as expected, with the engine not running but ignition on.

I had the wrong relay installed (as received from PO). The number is 141 951 253B.

It had seemed to me that the DRLs worked some of the time, but not always. Based on Alan's explanation, it is likely that they were only on with the ignition on but engine not running.

Given this flaky behaviour I recently ordered a replacement from Roger. I had not installed it as I was trying to first solve the headlight issue, which I had assumed was independent.

The replacement lists as 431 951 253G. There is a big difference between the two:



The diode that Alan said is required on 85 is missing in the relay that was installed. The installed relay is the same as supposed to be in IV for the fogs according to the 929Int chart.

When I get a chance tomorrow I will go through all of the relays to make sure they are correct.

Meanwhile, I'm really happy. I had a frustrating afternoon yesterday and it is really nice to get this resolved. Many thanks to Alan for his invaluable diagnostic help, and to Jeff for travelling the same road and finding the answer.

Alan

The 928 Int'l chart is wrong - you just need a 53B in the foglights... either will work just fine but the 53B (or generic Hella/Bosch/Tyco) is much cheaper and more easily available everywhere...

Alan

andy-gts

so B or G. did the swap for 53 G solve the problem

ROG100

Martin did the DRL relay I supplied work? Trying to ensure we do not have a DRL relay issue as with Jeff's car.