Diagnostic tester can no longer communicate with the ABS & PSD ECU
10-03-2023, 08:29 AM
#1
Intermediate
Thread Starter
Diagnostic tester can no longer communicate with the ABS & PSD ECU
Diagnostic tester can no longer communicate with the ABS & PSD ECU
Applies to S4, GT and GTS
Having found no info on this on rennlist I am posting information and the solution to this problem for the benefit of the 928 community.
This happens if the PSD ECU thinks the engine is running as soon as the ignition is switched on.
The PSD ECU uses the alternator exciter circuit (known as terminal 61) as a way of detecting whether the engine is running. The +D term 61 signal is applied to pin 27 of the ABS & PSD ECU connector. When the ignition is on the exciter circuit is connected to the alternator field coils and the term 61 voltage is about 2V. When the engine is running the alternator puts 12V onto this circuit. If the alternator field coils become disconnected for any reason the PSD ECU thinks the engine is running as soon as the ignition is switched on, and a Diagnostic tester can no longer communicate with the ABS & PSD ECU. Another symptom of this is that the PSD light only flashes briefly at ignition on, whereas it should come on with ignition on and remain on until the engine is started. No warning is shown on the digi-dash.
The terminal 61 circuit runs as follows:
Blue wire from alternator +D term 61 terminal to engine bay 14-pin connector pin 1.
Engine bay harness from 14-pin connector pin 1 to CE panel connector E21.
CE panel internal connections from CE panel connectors E21 to G11 and V21.
From CE panel connector V21 to ignition monitoring relay pin 8.
From CE panel connector G11 to alarm system ECU pin 23.
From CE panel connector G11 to T23 connector pin 1 and to pin 13 of instrument cluster.
From T23 connector pin 1 to ABS & PSD ECU pin 27, and also to RDK ECU pin 22.
Failure of the blue alternator exciter wire is common, either near the alternator or at the engine bay 14-pin connector pin 1.
Jonathan 2023
Applies to S4, GT and GTS
Having found no info on this on rennlist I am posting information and the solution to this problem for the benefit of the 928 community.
This happens if the PSD ECU thinks the engine is running as soon as the ignition is switched on.
The PSD ECU uses the alternator exciter circuit (known as terminal 61) as a way of detecting whether the engine is running. The +D term 61 signal is applied to pin 27 of the ABS & PSD ECU connector. When the ignition is on the exciter circuit is connected to the alternator field coils and the term 61 voltage is about 2V. When the engine is running the alternator puts 12V onto this circuit. If the alternator field coils become disconnected for any reason the PSD ECU thinks the engine is running as soon as the ignition is switched on, and a Diagnostic tester can no longer communicate with the ABS & PSD ECU. Another symptom of this is that the PSD light only flashes briefly at ignition on, whereas it should come on with ignition on and remain on until the engine is started. No warning is shown on the digi-dash.
The terminal 61 circuit runs as follows:
Blue wire from alternator +D term 61 terminal to engine bay 14-pin connector pin 1.
Engine bay harness from 14-pin connector pin 1 to CE panel connector E21.
CE panel internal connections from CE panel connectors E21 to G11 and V21.
From CE panel connector V21 to ignition monitoring relay pin 8.
From CE panel connector G11 to alarm system ECU pin 23.
From CE panel connector G11 to T23 connector pin 1 and to pin 13 of instrument cluster.
From T23 connector pin 1 to ABS & PSD ECU pin 27, and also to RDK ECU pin 22.
Failure of the blue alternator exciter wire is common, either near the alternator or at the engine bay 14-pin connector pin 1.
Jonathan 2023
The following users liked this post:
Arnoud (10-03-2023)
10-03-2023, 09:32 AM
#2
Rennlist Member
Diagnostic tester can no longer communicate with the ABS & PSD ECU
Applies to S4, GT and GTS
Having found no info on this on Rennlist I am posting information and the solution to this problem for the benefit of the 928 community.
This happens if the PSD ECU thinks the engine is running as soon as the ignition is switched on.
The PSD ECU uses the alternator exciter circuit (known as terminal 61) as a way of detecting whether the engine is running. The +D term 61 signal is applied to pin 27 of the ABS & PSD ECU connector. When the ignition is on the exciter circuit is connected to the alternator field coils and the term 61 voltage is about 2V. When the engine is running the alternator puts 12V onto this circuit. If the alternator field coils become disconnected for any reason the PSD ECU thinks the engine is running as soon as the ignition is switched on, and a Diagnostic tester can no longer communicate with the ABS & PSD ECU. Another symptom of this is that the PSD light only flashes briefly at ignition on, whereas it should come on with ignition on and remain on until the engine is started. No warning is shown on the digi-dash.
The terminal 61 circuit runs as follows:
Blue wire from alternator +D term 61 terminal to engine bay 14-pin connector pin 1.
Engine bay harness from 14-pin connector pin 1 to CE panel connector E21.
CE panel internal connections from CE panel connectors E21 to G11 and V21.
From CE panel connector V21 to ignition monitoring relay pin 8.
From CE panel connector G11 to alarm system ECU pin 23.
From CE panel connector G11 to T23 connector pin 1 and to pin 13 of instrument cluster.
From T23 connector pin 1 to ABS & PSD ECU pin 27, and also to RDK ECU pin 22.
Failure of the blue alternator exciter wire is common, either near the alternator or at the engine bay 14-pin connector pin 1.
Jonathan 2023
Applies to S4, GT and GTS
Having found no info on this on Rennlist I am posting information and the solution to this problem for the benefit of the 928 community.
This happens if the PSD ECU thinks the engine is running as soon as the ignition is switched on.
The PSD ECU uses the alternator exciter circuit (known as terminal 61) as a way of detecting whether the engine is running. The +D term 61 signal is applied to pin 27 of the ABS & PSD ECU connector. When the ignition is on the exciter circuit is connected to the alternator field coils and the term 61 voltage is about 2V. When the engine is running the alternator puts 12V onto this circuit. If the alternator field coils become disconnected for any reason the PSD ECU thinks the engine is running as soon as the ignition is switched on, and a Diagnostic tester can no longer communicate with the ABS & PSD ECU. Another symptom of this is that the PSD light only flashes briefly at ignition on, whereas it should come on with ignition on and remain on until the engine is started. No warning is shown on the digi-dash.
The terminal 61 circuit runs as follows:
Blue wire from alternator +D term 61 terminal to engine bay 14-pin connector pin 1.
Engine bay harness from 14-pin connector pin 1 to CE panel connector E21.
CE panel internal connections from CE panel connectors E21 to G11 and V21.
From CE panel connector V21 to ignition monitoring relay pin 8.
From CE panel connector G11 to alarm system ECU pin 23.
From CE panel connector G11 to T23 connector pin 1 and to pin 13 of instrument cluster.
From T23 connector pin 1 to ABS & PSD ECU pin 27, and also to RDK ECU pin 22.
Failure of the blue alternator exciter wire is common, either near the alternator or at the engine bay 14-pin connector pin 1.
Jonathan 2023
While I don't have a PSD related issue this is very informative for my instrument cluster backlighting always on issue.
Kevin
10-03-2023, 11:07 AM
#3
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Failure of D+ (61) circuit causes the battery not to charge - so it's an obvious critical failure which must be fixed for normal functionality. The dash will Either*: stay in bulb test mode after start, or bulb test will cancel immediately after turning the ignition on. It does indeed affect many systems including some diagnostics, but it needs an urgent fix anyway in its own right.
* Which depends on the failure mode:
- (61) always stays low voltage (<3v) - caused by a short to ground on (61) or a specific regulator failure mode
OR
- (61) stays at ~12V with ignition on before start - caused by an open circuit on (61) - this is the most common failure, usually due to wire degradation at the alternator end - esp. mechanically caused (e.g. a dangling alternator)
The connection details shared are applicable directly only to '90+ cars, the connection points for (61) on earlier S4 cars are different.
Note that '87/'88 cars are not equipped with PSD and have only ABS with a smaller 35 pin connector (without any diagnostic capability). '89 was a transitional year with PSD an option, if PSD was optioned you had diagnostics in the new dual ABS/PSD controller with 55 pin connector, ABS only was still without diag. using the old 35 pin controller.
Alan
PS: Kevin where is the thread for your instrument cluster backlighting always on issue? (many years the backlighting Should be on with ignition).
* Which depends on the failure mode:
- (61) always stays low voltage (<3v) - caused by a short to ground on (61) or a specific regulator failure mode
OR
- (61) stays at ~12V with ignition on before start - caused by an open circuit on (61) - this is the most common failure, usually due to wire degradation at the alternator end - esp. mechanically caused (e.g. a dangling alternator)
The connection details shared are applicable directly only to '90+ cars, the connection points for (61) on earlier S4 cars are different.
Note that '87/'88 cars are not equipped with PSD and have only ABS with a smaller 35 pin connector (without any diagnostic capability). '89 was a transitional year with PSD an option, if PSD was optioned you had diagnostics in the new dual ABS/PSD controller with 55 pin connector, ABS only was still without diag. using the old 35 pin controller.
Alan
PS: Kevin where is the thread for your instrument cluster backlighting always on issue? (many years the backlighting Should be on with ignition).
10-03-2023, 11:56 AM
#4
Rennlist Member
Failure of D+ (61) circuit causes the battery not to charge - so it's an obvious critical failure which must be fixed for normal functionality. The dash will Either*: stay in bulb test mode after start, or bulb test will cancel immediately after turning the ignition on. It does indeed affect many systems including some diagnostics, but it needs an urgent fix anyway in its own right.
* Which depends on the failure mode:
- (61) always stays low voltage (<3v) - caused by a short to ground on (61) or a specific regulator failure mode
OR
- (61) stays at ~12V with ignition on before start - caused by an open circuit on (61) - this is the most common failure, due to wire degradation at the alternator end - esp. mechanically caused (e.g. a dangling alternator)
The connection details shared are applicable directly only to '90+ cars, the connection points for (61) on earlier cars are different.
Note that '87/'88 cars are not equipped with PSD and have only ABS with a smaller 35 pin connector (without any diagnostic capability). '89 was a transitional year with PSD an option, if PSD was optioned you had diagnostics in the new dual ABS/PSD controller with 55 pin connector, ABS only was still without diag. using the old 35 pin controller.
Alan
PS: Kevin where is the thread for your instrument cluster backlighting always on issue? (many years the backlighting Should be on with ignition).
* Which depends on the failure mode:
- (61) always stays low voltage (<3v) - caused by a short to ground on (61) or a specific regulator failure mode
OR
- (61) stays at ~12V with ignition on before start - caused by an open circuit on (61) - this is the most common failure, due to wire degradation at the alternator end - esp. mechanically caused (e.g. a dangling alternator)
The connection details shared are applicable directly only to '90+ cars, the connection points for (61) on earlier cars are different.
Note that '87/'88 cars are not equipped with PSD and have only ABS with a smaller 35 pin connector (without any diagnostic capability). '89 was a transitional year with PSD an option, if PSD was optioned you had diagnostics in the new dual ABS/PSD controller with 55 pin connector, ABS only was still without diag. using the old 35 pin controller.
Alan
PS: Kevin where is the thread for your instrument cluster backlighting always on issue? (many years the backlighting Should be on with ignition).
I didn't want to derail this thread.
Kevin
10-03-2023, 02:32 PM
#5
Intermediate
Thread Starter
Re Alan's >> The dash will Either*: stay in bulb test mode after start, or bulb test will cancel immediately after turning the ignition on. <<
My experience was that the above is NOT the case. Bulb test was normal except for the green PSD light, which only flashed briefly at ignition on instead of correctly staying on until engine start like the rest of the bulbs.
Regards,
Jonathan
My experience was that the above is NOT the case. Bulb test was normal except for the green PSD light, which only flashed briefly at ignition on instead of correctly staying on until engine start like the rest of the bulbs.
Regards,
Jonathan
10-04-2023, 05:39 PM
#6
Rennlist Member
Failure of D+ (61) circuit causes the battery not to charge - so it's an obvious critical failure which must be fixed for normal functionality. The dash will Either*: stay in bulb test mode after start, or bulb test will cancel immediately after turning the ignition on. It does indeed affect many systems including some diagnostics, but it needs an urgent fix anyway in its own right.
* Which depends on the failure mode:
- (61) always stays low voltage (<3v) - caused by a short to ground on (61) or a specific regulator failure mode
OR
- (61) stays at ~12V with ignition on before start - caused by an open circuit on (61) - this is the most common failure, usually due to wire degradation at the alternator end - esp. mechanically caused (e.g. a dangling alternator)
The connection details shared are applicable directly only to '90+ cars, the connection points for (61) on earlier S4 cars are different.
Note that '87/'88 cars are not equipped with PSD and have only ABS with a smaller 35 pin connector (without any diagnostic capability). '89 was a transitional year with PSD an option, if PSD was optioned you had diagnostics in the new dual ABS/PSD controller with 55 pin connector, ABS only was still without diag. using the old 35 pin controller.
Alan
PS: Kevin where is the thread for your instrument cluster backlighting always on issue? (many years the backlighting Should be on with ignition).
* Which depends on the failure mode:
- (61) always stays low voltage (<3v) - caused by a short to ground on (61) or a specific regulator failure mode
OR
- (61) stays at ~12V with ignition on before start - caused by an open circuit on (61) - this is the most common failure, usually due to wire degradation at the alternator end - esp. mechanically caused (e.g. a dangling alternator)
The connection details shared are applicable directly only to '90+ cars, the connection points for (61) on earlier S4 cars are different.
Note that '87/'88 cars are not equipped with PSD and have only ABS with a smaller 35 pin connector (without any diagnostic capability). '89 was a transitional year with PSD an option, if PSD was optioned you had diagnostics in the new dual ABS/PSD controller with 55 pin connector, ABS only was still without diag. using the old 35 pin controller.
Alan
PS: Kevin where is the thread for your instrument cluster backlighting always on issue? (many years the backlighting Should be on with ignition).
10-05-2023, 01:00 AM
#7
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Alan
Trending Topics
10-05-2023, 06:26 PM
#8
Rennlist Member
Alan,
I have seen the multiple option for sure on the harness of the 1990. There is only one for 1990 and it comes with Dual head connector (one for PSD equipped and one without and a specific mention of LSD instead of PSD). I also saw on RL at one point a J spec 928 with LSD and being a 1990 (even VIN confirmed so).
Like you said, could be a late model 89 availability… you never know with what parts Porsche tossed depending what was sitting on the parts bin
I have seen the multiple option for sure on the harness of the 1990. There is only one for 1990 and it comes with Dual head connector (one for PSD equipped and one without and a specific mention of LSD instead of PSD). I also saw on RL at one point a J spec 928 with LSD and being a 1990 (even VIN confirmed so).
Like you said, could be a late model 89 availability… you never know with what parts Porsche tossed depending what was sitting on the parts bin