Intermittant fault - Need help solving??
02-26-2012, 04:20 AM
#1
Burning Brakes
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Intermittant fault - Need help solving??
Hey guys.
Over the last couple of years my 993 has had an intermittent fault causing it to not start. Its only happened about 4 times in the last 2 years. When you turn the key there's literally nothing. Initially I thought it was the starter motor but now after reading a few threads I think it may be the immobilizer.
The last time was the first time I had to call AA as every other time after a bit of fiddling its started but this time it didn't. The AA guy was fairly up to speed and together we went through checking the battery, ignition switch etc and after not finding a fault we decided to crash start it while moving the car into a better position just before we went for the big push I turned the car and it started.
Its hard to explain all the other times and what did and didn't happen but after reading all the different possibilities I'm thinking its related to a bad connection as per the advice below by "ebstibi". Its generally been movement of the car that has enabled it to start again.
So with all this in mind where do I start to thoroughly check and clean the whole immobilizer system (I'm thinking with electrical cleaner). Any advice, pictures etc will be much appreciated.
Car is a 1996 US 993 C2
cheers KCG
Over the last couple of years my 993 has had an intermittent fault causing it to not start. Its only happened about 4 times in the last 2 years. When you turn the key there's literally nothing. Initially I thought it was the starter motor but now after reading a few threads I think it may be the immobilizer.
The last time was the first time I had to call AA as every other time after a bit of fiddling its started but this time it didn't. The AA guy was fairly up to speed and together we went through checking the battery, ignition switch etc and after not finding a fault we decided to crash start it while moving the car into a better position just before we went for the big push I turned the car and it started.
Its hard to explain all the other times and what did and didn't happen but after reading all the different possibilities I'm thinking its related to a bad connection as per the advice below by "ebstibi". Its generally been movement of the car that has enabled it to start again.
So with all this in mind where do I start to thoroughly check and clean the whole immobilizer system (I'm thinking with electrical cleaner). Any advice, pictures etc will be much appreciated.
Car is a 1996 US 993 C2
cheers KCG
I am quite late to the party but wanted to add some guidance that I recently documented when I troubleshot a starting issue. I agree with some of the posters that proper analysis should be made before jumping on replacing parts, in particular electronic boxes:
0. Swap DME relay with the spare I had in the glove box. Car did not give a single sound while starting -> rule out DME relay issue at the moment
1. Battery voltage 12.8 V and I switched it with the one from my second (starting) 993. Still no cranking or klicking from the solenoid -> battery ok
2. All connection at battery tight and mass band in trunk "looks like new" -> ruled out issues here at the moment
3. Switched Starter relay (R61) with a similar relay that knowingly works (e.g. horn that is easy to test). car still "dead while starting -> starter relay R61 ok
4. Pull starter relay R 61 and do the following measurements:
4.a Check pin 86 for 12V. This is the 12V from the immobilizer to the starter relay coil that acts as an interlock to start the car. In my case I got the 12 V when I opened the car properly and turned the ignition on within the required time. -> immobilizer ruled out as an issue
4.b. Check pin 85 for proper mass signal (resistance measurement against mass). MJ 97 and later have a clutch switch that provides the mass to the starter coil switch. I measured "0 Ohm" with depressed clutch -> ruled out clutch switch
The previous measurements confirmed that the starter relay coil gets the proper supply. No to the power side of R61
4.c. Check pin 30 for 12V with the ignition switch turned to position 3 (start position to crank). I measured 12 V. -> ruled out ignition switch issue
The previous measurement confirmed that the power side of the R61 gets the proper signal too (12V). This all ruled out any relay related issues "in the trunk". I than moved to the starter and its connections as I assumed that an issue with the cable that provides the switched 12 V from starter relay power side to the starter solenoid is not likely.
5. Checked starter for tight and clean connections. Need to include the mass connection at the chassis side -> everthing was thight and clean like new -> IT MUST BE THE STARTER
6. Replaced starter -> car starts as it is suppsed to start!
Bottomline is as Steve already said: Root causes can be multiple and proper and "cheap" diagnosis before replacing expensive parts like Immobilizer unit can safe both time and money.
Here is the list of potential issues again that can lead to a car not starting "from the electrical side" and I am sure there is more when you include general "cable issues" between working components.
1. DME relay
2. Battery
3. Battery connections
4. Starter Relay R61
5. Immobilizer Unit / maybe key fob if you are lucky
6. Clutch switch (for MJ 97 and 98)
7. Ignition switch
8. Connections to starter
9. starter itself
Good Luck!
0. Swap DME relay with the spare I had in the glove box. Car did not give a single sound while starting -> rule out DME relay issue at the moment
1. Battery voltage 12.8 V and I switched it with the one from my second (starting) 993. Still no cranking or klicking from the solenoid -> battery ok
2. All connection at battery tight and mass band in trunk "looks like new" -> ruled out issues here at the moment
3. Switched Starter relay (R61) with a similar relay that knowingly works (e.g. horn that is easy to test). car still "dead while starting -> starter relay R61 ok
4. Pull starter relay R 61 and do the following measurements:
4.a Check pin 86 for 12V. This is the 12V from the immobilizer to the starter relay coil that acts as an interlock to start the car. In my case I got the 12 V when I opened the car properly and turned the ignition on within the required time. -> immobilizer ruled out as an issue
4.b. Check pin 85 for proper mass signal (resistance measurement against mass). MJ 97 and later have a clutch switch that provides the mass to the starter coil switch. I measured "0 Ohm" with depressed clutch -> ruled out clutch switch
The previous measurements confirmed that the starter relay coil gets the proper supply. No to the power side of R61
4.c. Check pin 30 for 12V with the ignition switch turned to position 3 (start position to crank). I measured 12 V. -> ruled out ignition switch issue
The previous measurement confirmed that the power side of the R61 gets the proper signal too (12V). This all ruled out any relay related issues "in the trunk". I than moved to the starter and its connections as I assumed that an issue with the cable that provides the switched 12 V from starter relay power side to the starter solenoid is not likely.
5. Checked starter for tight and clean connections. Need to include the mass connection at the chassis side -> everthing was thight and clean like new -> IT MUST BE THE STARTER
6. Replaced starter -> car starts as it is suppsed to start!
Bottomline is as Steve already said: Root causes can be multiple and proper and "cheap" diagnosis before replacing expensive parts like Immobilizer unit can safe both time and money.
Here is the list of potential issues again that can lead to a car not starting "from the electrical side" and I am sure there is more when you include general "cable issues" between working components.
1. DME relay
2. Battery
3. Battery connections
4. Starter Relay R61
5. Immobilizer Unit / maybe key fob if you are lucky
6. Clutch switch (for MJ 97 and 98)
7. Ignition switch
8. Connections to starter
9. starter itself
Good Luck!
02-26-2012, 11:48 AM
#2
Rennlist Member
Has the starter been well used? .... high miles, or a lot of short start/stops in town?
When it does kick in, does it do so with enough torque to seriously spin the engine .... or is it a bit lame?
When it failed to kick in, was it a on a hot or cold engine? .... or both?
Obviously, my attention is (currently) [pardon the electrical pun] on the starter: I recently replaced one on our 1.8T Passat .... it quit without any solenoid clicks or clashing from a worn bendix drive, and had me thinking initially it was a failed ECU module .... car started with a push & drop of clutch ... ergo - starter.
Brushes were worn down to the point that the motor would spin with key to start position .... but not adequate amperage transfer to bring it up the "starting" speed: $80 for a new brush set installed - spins great.
When it does kick in, does it do so with enough torque to seriously spin the engine .... or is it a bit lame?
When it failed to kick in, was it a on a hot or cold engine? .... or both?
Obviously, my attention is (currently) [pardon the electrical pun] on the starter: I recently replaced one on our 1.8T Passat .... it quit without any solenoid clicks or clashing from a worn bendix drive, and had me thinking initially it was a failed ECU module .... car started with a push & drop of clutch ... ergo - starter.
Brushes were worn down to the point that the motor would spin with key to start position .... but not adequate amperage transfer to bring it up the "starting" speed: $80 for a new brush set installed - spins great.
