R129 Newbie Questions...

[Johnniek]

Dear all

Just picked my 1998 SL500 which is lovely. However a few (related?) faults appeared on the journey home... any ideas?

1. Climate was working well but I pressed the 'EC' button and now it won't go back to normal Air Conditioned air. Mechanic checked the system pressure and all is good. Could an ECU / pressure sensor be at fault? All other functions are fine.

2. Interior lights (both map reading lights) don't come on with doors, switch set as it should be, puddle and footwell lights all work fine..

3. Radio no longer has any bass, only treble is working, tone settings all normal (it's the stock MB head unit).

Would welcome any inspiration

Thanks JK

 

[IanA2]

Dear all

Just picked my 1998 SL500 which is lovely. However a few (related?) faults appeared on the journey home... any ideas?

1. Climate was working well but I pressed the 'EC' button and now it won't go back to normal Air Conditioned air. Mechanic checked the system pressure and all is good. Could an ECU / pressure sensor be at fault? All other functions are fine.

2. Interior lights (both map reading lights) don't come on with doors, switch set as it should be, puddle and footwell lights all work fine..

3. Radio no longer has any bass, only treble is working, tone settings all normal (it's the stock MB head unit).

Would welcome any inspiration

Thanks JK

129 V8's are nice cars

When you say the a/c is not working, iirc the light is counter intuitive. Lit when off and out when on. In any case (some folks will differ) I've never found the a/c in 129's to be that wonderful (bit like the rear window heater).

Have you checked the position of the switches for your reading lights iirc there are three positions. Off, on when door is open and on.
Can't help with the radio (If I've helped at all)

 

[BTB 500]

What Ian said!

 

[Johnniek]

Hi
Yes deffo EC button is still stuck on, having read handbook it is behaving as if AC system pressure has leaked, hence my concern that pressure sensor might be faulty or AC ECU?

Interior light switches deffo in correct position for 'illuminate with doors open'

Thanks JK

 

[BTB 500]

Re. the interior lights, check the fuses (what else is on the same fuse). Can't be door switches if the puddle lights come on.

 

[norfolkngood]

Good luck with fixing these.

My newly acquired 129 (SL 300) is living in the garage after a 140 mile drive home. Starting to work up a snagging list of stuff I'll need to fix including a "quiet" horn - not normally something I'd check on a test drive.

 

[James]

Doesn't the light stay on if there is an AC fault if it is an EC button? If it is a snowflake/AC button and there is a fault the light wont come on when pressed??

 

[jjrodger]

Air con
The air conditioner has a diagnostic mode accessed thus:

1. Turn ignition on (without firing engine)

2. Set the air con temp to 72 deg F or 22 deg C

3. Press "REST" for more than 6 seconds

4. The left side of the display will alternately display "01" (which is the test number) and the cabin interior temperature (eg 72 deg F or whatever the temp in the car happens to be).

5. Press the fan speed "+" button to advance to the next test (eg "02").

The tests on the push button control unit are great:

01 In-car temperature sensor °C
02 Outside temperature sensor °C
03 Left heat exchanger temp. sensor °C
05 Evaporator temperature sensor °C
06 Coolant temperature sensor °C
07 Refrigerant pressure bar
08 Refrigerant temperature sensor °C
09 Not assigned --
10 Blower control voltage Volt
20 Auxiliary fan control current mA
21 Engine Speed x100 RPM
22 Vehicle Speed km/h
23 Circuit 58d (% of batt. Voltage) %
24 Battery Voltage Volt
40 Software staus
41 Software staus
42 Variant Code 1st numerical value
43 Variant Code 2nd numerical value
50 Not assigned
51 Not assigned
52 Not assignd
60 Roof OPE/CLO
61 Left side air outlet, knurled wheel
potentiometer Volts
62 Vacuum actuator 46, feedback
potentiometer Volts
63 Center outlet, knurled wheel
potentiometer Volts
64 Vacuum actuator 47, feedback
potentiometer Volts
65 Right side air outlet, knurled wheel
potentiometer Volts
66 Vacuum actuator 48, feedback
potentiometer Volts

If you do a bit of interneting you should be able to obtain a full list plus the appropriate values.

Interior lights
I had precisely the same problem with my interior lights. Replacing the light switch (on - off - on when door open) cured the fault. Be careful when removing and reinstalling dome light as the plastic housing can crack easily.

Stereo
It sounds like you have a fault with the power supply to the amplifier. I wonder whether there is a blown fuse either in the fuse box or on the amplifier itself.

 

[Johnniek]

Thanks for this info. I did some web searches and couldn't find values sadly. I note that this CC can display error codes on other models, I guess this is not readable on a 98 R129?

Will follow up on the other leads, will check fuses and switch.

Your help is much appreciated

Cheers JK

 

[Johnniek]

I did find this, will try in the morning....

 

[jjrodger]

I can't help you with values or the air con diagnostic, I am afraid. It could be a bad sensor. Are the exterior temperature and cabin temperature both low? If so, it may be that the system simply doesn't think cooling is called for.

The other thing I have seen is the push button mechanism breaking. The plastic goes brittle with age and the button ceases to work. It would feel odd if this were the case.

 

[Johnniek]

Hi
I can report back that I managed to read and clear the fault codes. Air con working again now. Will see if it what happens.

I located the power amp for radio, unplugged and re plugged and still no bass. I check the fuses and the radio / amp appear to be on the same circuit? Couldn't see any fuse on the under rear seat box (photo attached). Could there be one in the boot? Couldn't find the rear fuse box... Any ideas?
I might try and extract the radio itself just in case wiring is loose?

 

[Johnniek]

Any thoughts on the ongoing radio issue? Cheers JK

 

[s12obh]

May sound silly but check bulb as well, known them to blow, if it does turn out to be that simple you have a cheap and easy fix hopefully.

 

[Jack Lockwood]

Any more info on the interior lights?

I have the same problem on my 92 500SL.

I've removed the dome light assembly and performed a continuity test on the switch. It seemed to be functioning ok on all positions.
I know both the door switches are working because of activation of well lights and lights on warning buzzer sounding.

Some info as to how it should function would also help..

I assume that the lights should come on when doors unlocked?
Do the lights dim off or just switch off?

I read about repairing a diode on module n2/4. I don't think this is applicable though as it only seems to be for US spec cars and the symptoms of that are slightly different, the issue they had was that the dome light came on with passenger door but not with the drivers door.

I also know that on other German cars the dimmer assembly is incorporated into the vacuum pump.
Do the lights get a trigger from the central locking to activate lights on unlock?

Any and all help will be welcomed..

I have had the car for about 5 months and I'm slowly working through the problems. Anybody who could give me more info on the seals for the hardtop, where to buy etc.. Will be handy also.

Many thanks, Jack

 

[Johnniek]

Just picking upon this thread.
Still not managed to sort out the radio issues, amp is still intermittent. However I was wondering which head units are compatible with the under rear seat Becker amp? I have the cassette radio & cd changer 'special' unit. Do any others with CD head units 'drop in' as replacements?

 

[Pcn1]

Hi all,

Came across this old thread and needed some similar advice.
Open the doors and the footwell lights come on but the reading lights (or dome lights?) dont. Checked the selector switch, and when I try and switch it to position 1 (left side as per hand book) ie come on with the doors, it dosnt stay there, it just fall back to the middle (like a momentary switch if you understand the term). Id assume the switch would physically stay in the position its moved too.
Has me thinking the swich mechinism has failed and it needs replacing.
Any thoughts, and where is the best place to buy said swithch, dealer ?

Thanks

 

[Doodle]

Yes, the switch should stay put. Breakers generally don't seem to disassemble the dome lights so you might stand a better chance going to the dealer.