ML500 ABS & ESP light are on, can't really back up car, happens when very wet outside

Question edited to add maker.
Question moved to model category.

It appears to be a known issue. You need an auto electrician with a pro grade scan tool computer to read all the codes.

https://www.google.com/search?q=2006+ML500+DSR+Malfunction+warning

https://www.google.com/search?q=auto+electrician+near+me

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TDISLine 1874 solutions Jun 16, 2012
The ESP system means the Electronic Stability Program. If the ESP lights on the dashboard permanently the ESP system is faulty.
You should access the ESP Electronic Control Unit (ECU) memory for pull out all DTC (Diagnostic Trouble Codes), using diagnostic equipment connected to the data link connector of the car. Then you will be full informed about bad pieces (e.g.: brake pedal switch, front right wheel abs sensor interrupted, ...). After bad pieces replacement you will be able to erase all faults memored by ESP ECU, in other words reset the ESP system and turn off the warning lamp on dashboard.

Check & replace if necessary the brake pedal switch placed above pedals on the support.
If the problem still occurs you should access the ABS & ESP ECU (Electronic Control Unit) using diagnostic equipment connected to the data link connector of the car, in order to pull out all DTC (Diagnostic Trouble Codes) memored.
Then you will be able to replace bad piece(s) and fix the problem by erasing all DTC stocked inside ABS & ESP ECU, and reset it.

The ESP system means the Electronic Stability Program. If the ESP lights on the dashboard permanently the ESP system is faulty.
You should access the ESP Electronic Control Unit (ECU) memory for pull out all DTC (Diagnostic Trouble Codes), using diagnostic equipment connected to the data link connector of the car. Then you will be full informed about bad pieces (e.g.: brake pedal switch, front right wheel abs sensor interrupted, ...). After bad pieces replacement you will be able to erase all faults memored by ESP ECU, in other words reset the ESP system and turn off the warning lamp on dashboard.

Check & replace if necessary the brake pedal switch placed above pedals on the support.
If the problem still occurs you should access the ABS & ESP ECU (Electronic Control Unit) using diagnostic equipment connected to the data link connector of the car, in order to pull out all DTC (Diagnostic Trouble Codes) memored.
Then you will be able to replace bad piece(s) and fix the problem by erasing all DTC stocked inside ABS & ESP ECU, and reset it.

The ESP system means the Electronic Stability Program. If the ESP lights on the dashboard permanently the ESP system is faulty.
You should access the ESP Electronic Control Unit (ECU) memory for pull out all DTC (Diagnostic Trouble Codes), using diagnostic equipment connected to the data link connector of the car. Then you will be full informed about bad pieces (e.g.: brake pedal switch, front right wheel abs sensor interrupted, ...). After bad pieces replacement you will be able to erase all faults memored by ESP ECU, in other words reset the ESP system and turn off the warning lamp on dashboard.

Check & replace if necessary the brake pedal switch placed above pedals on the support.
If the problem still occurs you should access the ABS & ESP ECU (Electronic Control Unit) using diagnostic equipment connected to the data link connector of the car, in order to pull out all DTC (Diagnostic Trouble Codes) memored.
Then you will be able to replace bad piece(s) and fix the problem by erasing all DTC stocked inside ABS & ESP ECU, and reset it.

Check & replace if necessary the brake pedal switch placed above pedals on the support.
If the problem still occurs you might access the ESP & ABS ECU (Electronic Control Unit) using diagnostic equipment connected to the data link connector of the car, in order to pull out all DTC (Diagnostic Trouble Codes) memored.
Then you will be able to replace bad piece(s) and fix the problem by erasing all DTC stocked inside ESP & ABS ECU & reset it.
I'm convinced that your brake pedal switch is faulty because the glow plug warning light went ON, along with the ESP & ABS. Just replace the brake pedal switch, see if rear stop lamps light when press the brake pedal, and test the car on the road.

Check & replace if necessary the brake pedal switch placed above pedals on the support.
If the problem still occurs you might access the ABS & ESP ECU (Electronic Control Unit) using diagnostic equipment connected to the data link connector of the car, in order to pull out all DTC (Diagnostic Trouble Codes) memored.
Then you will be able to replace bad piece(s) and fix the problem by erasing all DTC stocked inside ABS ECU & reset it.

The ESP system means the Electronic Stability Program. If the ESP lights on the dashboard permanently the ESP system is faulty. You must access the ESP Electronic Control Unit (ECU) memory for pull out all DTC (Diagnostic Trouble Codes), using diagnostic equipment connected to the data link connector of the car. Then you will be full informed about bad pieces (e.g.: brake pedal switch, front right wheel abs sensor interrupted, ...). After bad pieces replacement you will be able to erase all faults memored by ESP ECU, in other words reset the ESP system and turn off the warning lamp on dashboard.
I'm convinced that your brake pedal switch is faulty because the glow plug warning sign went ON after ESP warning light. Just replace the brake pedal switch, see if rear stop lamps light when press the brake pedal, and test the car on the road.
Good Luck!

The ESP system means the Electronic Stability Program. If the ESP & ABS lights on the dashboard permanently the ESP & ABS system is faulty. You must access the ESP & ABS Electronic Control Unit (ECU) memory for pull out all DTC (Diagnostic Trouble Codes), using diagnostic equipment connected to the data link connector of the car (placed in dashboard, under a plastic cover above the ashtray). Then you will be full informed about bad pieces (e.g.: front right wheel abs sensor interrupted, ...). After bad pieces replacement you will be able to erase all faults memored by ESP & ABS ECU, in other words reset the ESP & ABS system and turn off the warning lamp on dashboard.

My Answer:

It appears that very possibly you have a bad ABS wheel sensor either up front (right or left side) if you only have Disc Brakes in the front and drum brakes in the rear, or else a bad ABS sensor in one of the rear wheels with a 4 wheel Disc Brake system.

The damp part was the giveaway, as if it's doing it in dampness then surely it'll do it when wet as well. That is a given!

Esp if it's not doing it in DRY weather.

If it's not a bad (leaky as from moisture getting inside it) ABS wheel sensor then it could just be chaffed wires coming off from one of the wheel sensors that's shorting to ground. Esp when it gets wet as from dew point moisture or from rain. Possibly, but somewhat doubtful.

If you just had the brakes serviced recently, and the problem started shortly there afterwords then I would definitely suspect the (a) wheel sensor.

If it's been a problem from DAY ONE, or even under the original warranty period then it needs to be fixed for FREE under that original warranty. No bones about it.

What's probably happening is that the sense wire from whichever wheel sensor is bad is shorting out and causing the ABS FAULT LIGHT to come on. I seriously doubt that you will get a CHECK ENG code fault, as this is purely a BRAKE ABS fault.

One thing you might do is pull the main wiring harness connector off of the ABS unit itself and check it for MOISTURE on the contacts. If any is found then that is your problem point.

Even if no moisture is spotted get a can of waterproofing spray from you local automotive parts store and spray out both sides of the ABS wiring harness connectors.

Since this is purely a MOISTURE related ABS Warning Light issue/problem it has to be one or the other and nothing else.

Sometimes it's best to check for this issue at night with a good bright LED type light, as then the MOISTURE will show up better then in the daytime.

If this fixes the problem please post the result.

Frank

My Answer:

It appears that very possibly you have a bad ABS wheel sensor either up front (right or left side) if you only have Disc Brakes in the front and drum brakes in the rear, or else a bad ABS sensor in one of the rear wheels with a 4 wheel Disc Brake system.

The damp part was the giveaway, as if it's doing it in dampness then surely it'll do it when wet as well. That is a given!

Esp if it's not doing it in DRY weather.

If it's not a bad (leaky as from moisture getting inside it) ABS wheel sensor then it could just be chaffed wires coming off from one of the wheel sensors that's shorting to ground. Esp when it gets wet as from dew point moisture or from rain. Possibly, but somewhat doubtful.

If you just had the brakes serviced recently, and the problem started shortly there afterwords then I would definitely suspect the (a) wheel sensor.

If it's been a problem from DAY ONE, or even under the original warranty period then it needs to be fixed for FREE under that original warranty. No bones about it.

What's probably happening is that the sense wire from whichever wheel sensor is bad is shorting out and causing the ABS FAULT LIGHT to come on. I seriously doubt that you will get a CHECK ENG code fault, as this is purely a BRAKE ABS fault.

One thing you might do is pull the main wiring harness connector off of the ABS unit itself and check it for MOISTURE on the contacts. If any is found then that is your problem point.

Even if no moisture is spotted get a can of waterproofing spray from you local automotive parts store and spray out both sides of the ABS wiring harness connectors.

Since this is purely a MOISTURE related ABS Warning Light issue/problem it has to be one or the other and nothing else.

Sometimes it's best to check for this issue at night with a good bright LED type light, as then the MOISTURE will show up better then in the daytime.

If this fixes the problem please post the result.

Frank