Trying to connect obd reader to an AGG installation; The OBD connector is stashed under the dash (so I assume that this means it is probably connected via the immobiliser?) (as you can tell, this was not my install);
I am seeing 12V on the 12V line, gnd on ground, and 12V on the K-line when the ignition is on.
But the OBD reader is not happy with something - I get the 'failed to communicate' error when it tries to connect.
Connecting a scope to the K-line I can see it being pulled low by the OBD Reader as it tries to set up the initial comms - so things look like they are attempting to work but I'm not getting any comms back from the ECU.
Anyone got anything that I can do to debug?
Should I be seeing 12V on the K-line (with ignition on, but OBD reader not connected)?
Only have 3 wires on the OBD connector - 12V, Chassis gnd and K-line (i.e. no signal ground)
I am doing this with ignition on, but engine not running.
Help please?
OBD Comms not working
Moderators: User administrators, Moderators
-
MidLifeCrisis
- Registered user
- Posts: 566
- Joined: 20 Nov 2011, 19:07
- 80-90 Mem No: 10519
- Location: Bagshot, Surrey
OBD Comms not working
1987 Westfalia Van, Petrol 2.0 AGG
-
Robsey
- Registered user
- Posts: 1171
- Joined: 19 May 2012, 20:45
- 80-90 Mem No: 11137
- Location: East Manchester
Re: OBD Comms not working
Is it the 16-pin eobd / eobd2 connector,
Or an earlier version for connection to aldl / kwp type vehicles.?
If it is the 16 pin plug,
Then wiring should be
Ground on pins 4 and 5
KWP diagnostics / K Line on pin 7
Battery voltage on pin 16.
Pin 7 should be a signal, not a steady voltage.
Or an earlier version for connection to aldl / kwp type vehicles.?
If it is the 16 pin plug,
Then wiring should be
Ground on pins 4 and 5
KWP diagnostics / K Line on pin 7
Battery voltage on pin 16.
Pin 7 should be a signal, not a steady voltage.
1983 Tin Top with a poorly DF and 4 speed DT box.
1987 Electrics and a DJ engine.
Maybe one day I might get it finished
1987 Electrics and a DJ engine.
Maybe one day I might get it finished
-
MidLifeCrisis
- Registered user
- Posts: 566
- Joined: 20 Nov 2011, 19:07
- 80-90 Mem No: 10519
- Location: Bagshot, Surrey
Re: OBD Comms not working
Yeah - so pin 7 has a signal on it but I think it’s just the signal from the ‘reader’ - don’t seem to get any reply from the ecu.
Busy going down the rabbit hole of k-line protocol now - think I may regret starting this!!
Busy going down the rabbit hole of k-line protocol now - think I may regret starting this!!
1987 Westfalia Van, Petrol 2.0 AGG
-
Robsey
- Registered user
- Posts: 1171
- Joined: 19 May 2012, 20:45
- 80-90 Mem No: 11137
- Location: East Manchester
Re: OBD Comms not working
What are you using to do the diagnostics?
A hand held code reader?
Or a VAG / ELM type interface and laptop.
Non communications may not necessarily be the fault of the car.
I have used ELM, Autoscanner, VauxCom, and other device diagnostic units.
With them, it could be something as simple as the ignition not being on,
Or the interface USB or serial to USB not being configured to the correct "Port".
A hand held code reader?
Or a VAG / ELM type interface and laptop.
Non communications may not necessarily be the fault of the car.
I have used ELM, Autoscanner, VauxCom, and other device diagnostic units.
With them, it could be something as simple as the ignition not being on,
Or the interface USB or serial to USB not being configured to the correct "Port".
1983 Tin Top with a poorly DF and 4 speed DT box.
1987 Electrics and a DJ engine.
Maybe one day I might get it finished
1987 Electrics and a DJ engine.
Maybe one day I might get it finished
-
Club Joker
- Registered user
- Posts: 14
- Joined: 10 Oct 2011, 21:52
- 80-90 Mem No: 8367
Re: OBD Comms not working
I had a similar problem with the OBD on my AGG conversion. Socket is at the front on mine and wired through the immobiliser as it is in the Golf. Worked fine using VCDS, but just stopped communicating one day.
Lots of messing around, new leads, com port reconfiguration etc. And still no luck.
Finally got it working again by jumping the k line in and out on the little connector that plugs into the immobiliser. You can either start the engine and then disconnect the small 6 pin connector from the immobiliser and jump the two k lines on the connector itself (paperclip or similar between the two connector points). VCDS should then connect as normal. Engine will continue to run without the immobiliser connected.
Alternatively you can jump the two wires across the back of the connector and keep the immobiliser connected. Bit more fiddley as you need a smaller wire, but can be left in place if insulated and the immobiliser seems to work fine almost all of the time, but occasionally seems to want the jumper disconnected. Took me 2 years to work this out!
Let me know if you need a picture. From memory it is the two grey wires on the immobiliser plug.
Lots of messing around, new leads, com port reconfiguration etc. And still no luck.
Finally got it working again by jumping the k line in and out on the little connector that plugs into the immobiliser. You can either start the engine and then disconnect the small 6 pin connector from the immobiliser and jump the two k lines on the connector itself (paperclip or similar between the two connector points). VCDS should then connect as normal. Engine will continue to run without the immobiliser connected.
Alternatively you can jump the two wires across the back of the connector and keep the immobiliser connected. Bit more fiddley as you need a smaller wire, but can be left in place if insulated and the immobiliser seems to work fine almost all of the time, but occasionally seems to want the jumper disconnected. Took me 2 years to work this out!
Let me know if you need a picture. From memory it is the two grey wires on the immobiliser plug.