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Discussion Starter #1
hi i have a 1990 r129 mercedes 300sl im getting code 28 no vehicle speed signal and code 30 roof blocked due to code 28 the speedo doesnt work ive checked abs sensors they seem fine was wondering if gearbox speed sensor is relevant to my problem any help would be great
 

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Does anyone have any ideas where the speed signal comes from there's 2 abs sensors 1 in each front and 1 rear sensor in diff there's also a sensor on rear of gear box my speedo is dead I've spent hours and hours on this and I'm stumped now cars of road as it can't pass mot without a speedo surely someone on the site must have an idea or had same prob in past maybe the 2 front abs sensors read 1030 ohms each the rear abs sensor reads 700 ohms gearbox sensor reads 1800 ohms


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Greek God of the R129
SL500-500SEL-190E
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The gear sensor goes in to the park neutral start harness, and I think to the top control ABS module.
From there to the speedometer.

Do a search about 6 months a go I helped a guy from UK.
I don't remember his code name.
Had a sensor/harness problem.

I think that his problem relates to yours.
If he sees your post I hope that he may comment/help.

Regards,
aam.
 

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Discussion Starter #4 (Edited)
thanks for the reply aam ive just bought the car it has the dreaded dash flash i replaced all capacitors in r129 cluster with 2 100 35v and a 420 35v capacitor made no differance so i popped the cluster from my w140 in and that seems to have got things going again untill i get r129 cluster repaired with dash flash nothing worked just the temp gauge now with w140 cluster everything works except speedo and car generates a code 28 no speed signal i have a spare gearbox speed sensor but they both read identical in ohms test dont have access to a scope to check waveform so assumed sensor is good as i didnt want to start cutting and splicing wires to swap out the sensor just yet why couldnt mercedes put a connector on them and make them more accessible
 

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problem now sorted

please don't believe posts that say the w140 clusters are interchangeable with the r129s they arnt the w140 has a 100 litre tank the r129 has 80 litre so the w140 fuel gauge seriously over reads up to nearly a quarter you will run out of fuel way before the gauge ever gets to empty

worst of all the speedo and mpg gauge wont work everything else seems to work ok but the above fault will add up to roof being disabled due to no speed signal from cluster also found that the speed signal comes from the gear box speed sensor and the left front wheel they work in tandem with the cluster to give the roof the signals it needs to allow safe operation

there's not a lot available in google searches so hope someone benefits from this information
 
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