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Registered 2001 SLK230
61 Posts
Discussion Starter #1

R170 2001 first flashed up the check engine light. So I bought an OBD-II tool which showed error P0720 and P0500.
Then soon thereafter, five warning lights popped up and a new error code P0600.

1. Brake pads worn down
2. Check engine
3. Brake Fluid Low (or handbrake on)
4. BAS malfunction / ESP malfunction
5. ABS malfunction

When these came on, the car switched to limp home mode... 2nd gear, no speedometer.

So after a lot of internet searching, I decided to remove the front wheels and check the front pads. They were at 5mm, which is the depth at which the sensor triggers a warning. I unplugged the brake pad sensor wires and put the wheels back on. I then used my OBD-II to reset the error codes and took it for a test drive. No warning lights, no errors. I stopped by both the best mechanic on the island and the auto electrician who agreed with likely diagnosis, saying how a single minor error can light up the dash like a Christmas tree and toss in limp mode.

As it happens, I am flying to the US in a few days, so will order front & rear pads, sensor wires and brake light switch from Pelican because they have such a helpful web site (and way better prices than down under).

It seems a poor design to drop the car into limp mode when the brakes have 5mm left on them, and the erroneous warnings (like brake fluid low... it was not) almost seem to be designed to drive business at the dealer.

In another posting, someone asked if the R170 would become a classic, collectible. I would say with the electronic systems and the potential extreme costs when something goes wrong (I was lucky), the era of collectibles may be over. The R170 is a fun car and I love the vario roof, but unlike my 1982 G-Wagon, electronics can be a financial nightmare.

Anyway, for the next person to encounter these symptoms, pull your wheels, inspect the pads, and if they are close to 5mm disconnect the sensors. If the problem goes away after resetting the OBD then you know it's just the pads... but be sure to replace them.

Registered 2001 SLK230
61 Posts
Discussion Starter #2
Update on brake pads causing errors and limp mode

I ordered front and rear brake pads and 2 sensors from Pelican to be shipped to a friend's place in Baltimore. They arrived the day I did.
When I got home to NZ, I installed them. The instructions found on line make it sound complicated, it was very easy and I will list them below for future reference (note: my car is clean, no snow driving and probably little rain driving thus everything came apart easily).

Post Install Error Codes and Lights

When installed, I used OBD Auto Doctor (paid version) to remove the diagnostic trouble codes and clear the dash warning lights.
On the first test drive, error codes returned and all the warning lights came back on - including the one that says the brake pads were thin, which is wrong, and suggested the OBD needed to sort itself out.
I drove up our hill and the car went into limp mode (2nd gear, no speedo). The thought crossed my mind that I had something more severe, not the brakes - which was a worry
Came back to the garage, cleared the codes and took for a second test drive.
That was better, until I pressed the brakes harder and the ABS and BAS/ESP warning lights came on (but no OBD codes)
Did another full reset and took it for a very long drive.
No more issues

This suggests for those who have similar symptoms that after installing new pads, it takes the system a while to sort itself out.
The limp mode suggests that either the German engineers who designed it were overly cautious, or the greedy bean-counters instructed that it be programmed to drive unnecessary and overly expensive dealer business. The warnings, lights and disabling the car for a vehicle that had 5mm of pad left seems an excessive reaction.

In any case, for those of you who prefer to not enrich the dealers, especially when their estimate is 1/4 the value of the car, in the end, all that happened was that the brake pads had hit 5mm. All the lights, codes and disabling of the car were sorted by replacing pads and sensors.


The short form to remove and replace R170 (facelift) brake pads 230SLK (presumes some experience with this sort of work)

Start with the rear pads, they are easier because you do not unbolt the calipers; the pads just slide out.
- Use a punch to remove the pin holding the pads, Pelican provided new springs, so remove the old, but take a photo to remember how they fit (it's obvious)
- Use a screwdriver to depress the pads so the pistons retract in the caliper. Follow the usual warnings to not screw this one up and damage the piston.
. ~ Useful tip: Have someone watch the brake fluid to make sure it does not spill over into the engine
. ~ Useful tip: You may want to open the bleeder if you think there is junk in the fluid that could press back into the ABS and cause expensive damage
- Remove the pads, in my case, remove the backer plate (?) since the new ones did not have them, grease appropriately with the Pelican provided grease
- Insert new pads, spring and piston and then do the usual checks and testing as with any brakes.

Then go to the fronts where the caliper must be removed
- Remove the sensor wire. One end pops out, the other slides upward using needle-nose pliers.
- Use a T40 Torx tool to remove the sensor bracket. It accesses from the back so use a lighted mirror tool to see what you are doing
- Remove the retaining springs - take a photo to remember how they go back (it's obvious)
- Press the piston back (the new pads are thicker, won't fit if the piston sticks out), as above, noting it displaces more fluid and may cause your master cylinder to overflow - deal with appropriately (I used an air-bleeder to suck out excess fluid)
- Pop off the plastic caps that protect the 7mm allen (hex key) bolt that holds the calipers on. Remove the bolts
- Gently remove the caliper (use common sense to not damage anything), remove the pads and clean as needed
- Grease the new pad backing in all the right places, insert and bolt the calipers back on. Tighten to factory spec if you have a torque wrench
- The new springs are a bit fiddly, I used needle-nose pliers to get the ends into the holes and then lightly tapped them to seat properly
- Use locking fluid on the sensor bracket and bolt it back in
- Install the new sensor and then do the usual checks and testing as with any brakes

Registered 2001 SLK230
61 Posts
Discussion Starter #3
2nd Update

No joy. Gremlins came back.

While the brake pads needed replacement, and sensors at $1.50 each is sensible to replace, unfortunately, the dash kept lighting up after all new pads and front wear sensors replaced. Same five lights.

So next, it was off to the auto electrician on the island who has much more sophisticated OBD code reader than mine. For NZ$65, he reset all the codes, told me to take it home, drive it and come back in a week.

It did not take long. Next morning the lights came back on, the car went into limp mode. A few more tries, and on Monday, I drove it back to the sparky in limp mode (not a problem since we have a 50kph (30 mph) speed limit on the island.

The sparky's device showed a whole slew of error codes, but he explained that if something trips the ABS, it cascades, triggering other errors like brake pads worn (the pads are new). For novices to the R170 error code system, it is primitive unlike newer cars that tend to isolate the cause better. Unfortunately, I was not able to copy down the detailed error codes the Sparky's reader showed... far more than the three generic codes of my OBD-II reader.

The first suspect was the brake light switch (see Pelican).

After I left the sparky, about 2 km down the road, the lights came on again and I limped home.

I had ordered a switch from Pelican (Brake Light Switch, Brand: Genuine Mercedes-Benz Part #: 001-545-64-09-M22) when I ordered the pads so that I qualified for the $8.99 3-day shipping. Good move as getting one in NZ would cost more and take a lot longer.

Replaced the switch... very easy job (twist, remove, unplug - plug in-slot in-twist to lock).
Reset the OBD codes and to be safe did the L-R-L-R lock to lock reset as well.

Test run: no lights, no error codes, no limp mode. Could that have been the problem?

Stay tuned.


Premium Member 2001 SLK320/2000 SLK230
2,719 Posts
Hope it stays fixed and a comment: one of the things I look for in any scanner is either a PC interface or ability to e-Mail results to my home. Both Carly Pro and Torque Pro have this capability while the iCarSoft according to the review, does not.

Since Merc reports can be quite voluminous and detailed (first run on a 171 resulted in a 10 page .pdf from Carly), comparisons are needed to tell what has changed. I usually pull a report from my OBD-II cars every month or two and showed that my Jeep was a candidate for a recall long before the dash light appeared.

If you stay up on it then anything new can usually be traced to a single point failure. Key is to be able to identify the single point. For example with either a P0170 or P0173 I'd be looking at the lead O2 sensor on that bank. With both the first look is to the MAF. A good scanner can provide a live report on any or all of these.

Years ago when my job was engine and flight controls we use to have a very long hallway we could roll out the brush chart report and look for anomalies. Today it is a spreadsheet I can search for outliers but why so important to be able to keep a record of what happened and when.

ps first computer car I had was a 1984 Fiero. First scanner (a thermal printer) was for same and was the first car computer I reprogrammed a bit. R170 tells me A Lot in comparison.

Registered 2001 SLK230
61 Posts
Discussion Starter #5
Update #2

The next morning, the error lights came on within 200 m of the garage. I shut off the car, restarted and it went 1 km before all five lights lit up again and dropped it into limp mode. I shut it off again, used my OBD-II cheapo reader to clear the check engine light. After that it ran fine the rest of the day. This suggests the brake light switch was not the problem, but it could be something that goes away when the car is warm. Anyone have any ideas?

On my test ride, I then sought out a gravel road and stomped on the brakes. No ABS. And the ABS and BAS/ESP lights came on (as they should), but not the other three on the left. Shutting off cleared them.

Probably its time to jack up the car, pull the wheels and check the toner ring sensors for dirt. Hard to work out if I actually have a real mechanical problem or a sensor that is not working right.

Registered 2001 SLK230
61 Posts
Discussion Starter #6

One of the challenges using forums is finding answers that link symptoms to solutions. Many postings trying to find the answer, with many helpful hints, but no resolution. Now I am creating a new thread with all the evidence and the cause so the next person who has similar symptoms can learn from my experience. Spoiler: It was the ESP module.

2001 R170 RHD Japan (now in New Zealand)

It began when the dash lit up like a Christmas Tree and a check OBD-II reader gave three generic codes P0500 P0600 P0720

Lesson One: The idiot lights lie. These light say I need new brake pads, my hand brake is on, and there is something wrong with my engine. In fact, the defect was the ESP module.

Lesson Two: MB programs for panic. When the ESP module has a problem, it causes a cascade of other symptoms that the uninformed owner concludes are defects rather than intentionally programmed effects that are intended to scare the bejesus out of the driver. Speedo drops to zero, transmission locks into first or second gear, vario roof won't work, shifting neutral to drive or reverse bangs. Shutting off the engine clears some symptoms but they soon return. These effects are programmed by Mercedes, and frankly, I am amazed no one has sued them for putting people at real risk under certain circumstances.

Lesson Three: Mercedes has its own codes and those are the ones you need to know about. The generic codes are useless. You need to either buy a more expensive reader that will read the MB codes, or take it to an auto electrician who has good equipment. If you trust the MB dealer, they will have the best code reader. However, insist all you need is for them to clear the history, run the code reader and give you the report.

ABS/BAS&ESP/Brake on/Check Engine/Pads low dashboard lights on
Drops into limp mode
OBD2 Codes P0500 P0600 P0720

Going to various forums, I found suggestions for things to look at, and since they either happened to be needed, or were cheap enough to just do them, I did the following first...

  • Replaced all brake pads (they were at 5mm)
  • Replaced front ABS sensors (they cost US$1.50 each, so why not?)
  • Replaced brake light switch (in order to get 3-Day shipping from Pelican, I had to order $100, and folks say this switch does go bad, so I bought the MB brand one)
  • Cleaned toner rings and sensors on all 4 wheels
No joy so it was time to escalate

Additional symptoms now that I was paying more attention:

  • When cold it will light up as many as six times in the first few miles.
  • Turning the key off and on usually clears it, except for the check engine light.
  • But then when it warms up, it seems to sort itself out (but not always) suggesting it might be an electrical short that connects when warm.
I took it to the auto electrician who came up with the following codes (transcribed from a photo of his notes, see pic below). He thought it might be the ESP module.

This link Mercedes Benz SLK Forum - View Single Post - Help!! SLK32 ABS/Brake/EAS lights check engine does support that hunch.

Auto electrician codes

Electronic Selector Module
1876 Connection with Traction System Interfered
1867 Left Rear RMS signal (electrician commented that while the readout said it was not sending signal when parked, it showed it actually was sending signal when driving)
1860 Right Rear RMS signal

200F-004 Fault Stored in Comp [??? unreadable] N15/3 (Ect-[ECS] Control Unit) P0720

20205 -001 Con message from control light ESP
002 Variable Speed signal Impossible P0500 P0500

2027 Com message from control module N47/5
016 (ESP, SPS [PM2] OBOS control units signal interruption

C1000-032 Check Control Unit N47-5 (ESP BOS Module)
064 Check Control Unit N47-5 (ESP BOS Module)
128 Supply of N47-5

C1022-002 COM BUS Communcation [???]
004 COM BUS Communcation [???]

..1000 Control Unit N47-5 is defective
31041 CON Communication front TO Traction Module

C1025.01 CAN BUS ECM [???]
02 CAN BUS ABS [???]
04 Stop S/W [????}

There were a number of forum postings that were very definitive.

For example, this one said ""ESP module" usually refers to component N47-5 which is housed inside the engine bay fuse/relay box. This is the bad part when you get code C1000." Another forum, which I can't find right now, was even more emphatic. It said if you get C1000, your ESP module is bad.

What does bad mean? I found that answer here where Adaptel wrote:

I know this is an older thread, but I am going to post this reply because i just ran through this same nightmare and didn't want to shell out the huge money for an ESP module. My 2001 SLK320 was doing all the same things, Intermittent BAS/ESP, ABS, Brake, and (O) lights would come on, I would loose my speedometer, and the transmission would be stuck in whatever gear it was in when the lights came on. If I put a standard codereader on it, I would get varying differnt codes, but the one that was always present was P0600 which was described as a "Serial Communications Link" failure.

To repair this, I had to open the ESP module, which is located on the driver's side (LHD) under the hood directly behind the ABS Pump block (has a bunch of brake lines going to it). You can remove the ESP module without disconnecting the brake lines by removing the connecter, then the 2 screws on the front of the whole module, then bend the whole assembly upward to access the four screws holding the ESP module to the hydraulic block. The black ESP box will then slide off of the block. Getting the ESP open is not easy because it is epoxied shut, but I came up with a cool trick to crack her open. if you put on a set of gloves, and use a torch to heat up the end of sharp razor knife, you can work it around the seam of the box to separate the cover from the main housing.

Once I had mine open, the problem was obvious. If you look at the solder joints using a bright light with a magnifying glass or microscope, check for cracked solder joints. They will show up as rings around the through-hole components. My box had a huge problem with the solder joints that went to the connector's pins. About 1/4 of them were degraded and the 4 larger pins (obviously carrying power to the high-current Abs solenoids) were really bad. I resoldered all the connector's pins and any others on the board that looked less than ideal, put the box back together using black adhesive silicone......and violla! I have not had an issue since then.

I have seen lots of reports of these symptoms and nobody ever seemed to post their solution. What was causing this is the ESP module was intermittantly losing power, which was causing one of the CAN serial busses to lock up and not allow other important data to reach the main brain (like wheel speeds, steering angle, etc). My problem was in the ESP module, and other places where this same serial bus hangs out is in the headlight switch, the ABS module, and the traction control module....which I am sure bad solder joints in these could cause identical symptoms. Hope this helps someone.

So armed with that information, I took the ESP module off. Unfortunately, there were no instructions I could find. So here is how I did it:

On RHD the ESP module is on the driver's side of the engine bay just in front of the fuse box. It is attached to a metal block with brake lines coming out of them, and on the other side of the shiny silver metal block is a round black ESP pump

The job is simple, except that the screws are weird and one is blocked by the fuse box

Remove the fuse box top for extra working room

4mm socket using small socket wrench

Wedge a piece of wood between the fuse box and the ESP module to give access the blocked screw. See pic

Remove all four screws that hold the module to the metal box.

Unplug the plug. Note that to do this, the retaining clip at the top must be moved 90 degrees away from the module, swinging it up.

Every instruction on line said disconnect the battery first. However, in thinking about it, if the key is off, not in the ignition, why should there be power going to it? I removed the key and hoped for the best. No sparks, no noise, it worked. Proceed at your own risk.

Remove the timber.

Separate the module by moving it toward the fuse box. You may have to push the metal block a bit, but it is flexible. It sits in three rubber grommets so it has wiggle room.

This is what it looks like:

I then had a choice. Buy new: $2,400. Take it to a specialist: $250 to solder it or find a good used part.

Silver Star Farm had a recently wrecked 2001 SLK. Module NZ$250, including block and pump. See pic:


On reinstall, the electrical socket would not go all the way in. Hint: Press the locking lever down to draw it the socket.

Screwed in the 4 screws
Fuse box cover back on
OBD-II reader cleared the codes
Standard reset procedures (google R170 reset)
Test drive: IT WORKS!


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