2009 C2S 186K miles

Describe how you shorted them out... all wheels or one at a time? More description please.

Peace
Bruce in Philly (now Atlanta)

 

One at a time, turning the ignition on after each, all 4 shorted (cut the wires and soldered them together, heat shrink, replace plug).

 

The "light", did you look in your manual for the exact display and read what it says? I can't really remember, but I think... not sure.... that you will get a different display if the system perceives a fault vs worn pads. Also, did you read the codes via your OBD port? Try running over to Autozone and let them read your codes for free if you don't have a reader.

You could also try starting your car, pull one of your shorting plugs out, insert the probes from your multimeter and measure voltage. I suspect it will be 12v like most everything else... but at a minimum, there should be voltage. If none, something is broken somewhere. Check your fuses?

Peace
Bruce in Philly (now Atlanta)

 

Thanks, it’s the brake wear illumination. I don’t have a code reader but no doubt I’ll be investing in one! I’ll try the circuit voltage check, good advice, at least that would indicate if there is a fault elsewhere in the circuit. Car is outside and it’s rainy here in Scotland so it will be tomorrow now. Thanks again

 

Another thing you could try in addition to checking voltage at a plug.

The system, as I understand it, is a singe cable going around to each wheel; a daisy chain. It is not a star-wired architecture. In other words, the system can't know which pad tripped the light. So... if you don't get voltage at one wheel, run a wire "outside" to another socket and then check for continuity and voltage... make sure you check for both. You will have to check each socket as I am not sure how they are wired in that loop. If there is a break in wire (again, it is a single run) and the break is in the wheel-to-wheel circuit, you should be able to isolate it.

It would then be great to check the point at which that wheel-to-wheel circuit is terminated but I don't know where that is. It may be at some computer module and not the dash binnacle.... there are a few in this car.

Peace
Bruce in Philly (now Atlanta)

 

Update! All sensors shorted, the issue remains BUT the warning light goes when the car is warmed up. This ties in with the instrument cluster gauges and outer LCDs - when it’s a cool temp outdoors and the car hasn’t been started, these gauges and LCDs flicker and eventually stay on after 8 - 10 mins…weird. Once they are all on, if I turn the car ignition off, then on, the brake pad wear warning light goes out. I’ve had the cluster out, no loose connections and nothing untoward on the PCBs. I am hoping someone else has experienced this, it may be a new cluster or at least a cluster indirection/repair?

 

Hi,

I am not sure if the 997 circuitry filosofy is the same as that from a 993.

In the 993 the light comes up when:
- the daisy chain is broken
- there is a short to ground in the chain

regards
Hans

 

From everything that has been written or reported on the 997, it is the same.

It would appear that a pull up resistor supplies 12V to one wire that must return via the other wire. Unplugging the sensor interrupts that circuit. Shorting either wire to ground also prevents the 12V from returning.

 

Delete

 

I'm having the exact same problem with same symptoms. Did you solve this?

 

The circuit is called a "dry contact'. It is just a signal. A voltage yes but no current. Trying to measure something you will get nothing. As stated above , when the sensor wears to the point of shorting out onto the rotor the chain is broken and no continuity thru the daisy chain.

 

These are known and accumulated faults that require repair of the instrument cluster. I can't find any explicit reference to the brake-wear indicator, but if it has been bridged on the instrument cluster and still appears, there is an indication -- imho.

• The LCD fields on the side show nothing
• With key out: indicator lights and display remain on, various communication errors.
• Airbaglight doesn't work when ignition on
• Airbag light does not work when ignition on, flickers intermittently or sporadically when instrument plug is wiggled.
• Temperature gauge does not work. Speedometer shows wrong values. Oil pressure gauge does not function.
• Airbag indicator light in instrument cluster without function.
• Water temperature indicator sometimes lights up red, sometimes not.
• Defective oil pressure indicator. The indicator is at 2.5 bar and is stuck. Even with the battery disconnected there is no change. Oil pressure sensor has already been replaced.
• Distance counter does not work / does not count.
• C177 Fault front control unit (comfort) 9151 Reverse light 2 failure

Fortunately, there are enough companies that specialise in repairs...
Edit: Post #21 points exactly to a problem with the instrument cluster...