gdallas
13-02-2019, 02:12 PM
Hi folks,
I’m trying to diagnose the source of the fault that VCDS is complaining about regards my G395 pressure sender;
00256 - A/C Pressure/Temperature Sensor (G395)
What I have done to date:
I have replaced the part with another OEM. But fault persists and instantly annunciates its self following a clear of DTC through VCDS.
I have traced the cables back visually as best I could given the current flow diagrams. Could not test continuity with built in DVM buzzer; presumably because the impedance was too great on the Lin Bus. But visually I see no defects or issues from the G395 sender > A pillar coupling station > A pillar coupling station > J519 module.
With the sender disconnected, I have verified a healthy 14V supply at the wiring loom connector into the G395 sender, similarly the ground is also good.
I have no means to test the validity of the data coming from the 3rd a final core, I.e. the Lin Bus, but what I can say is there is no short to gnd. With the sender disconnected I am able to measure at the connector, a voltage which fluctuates from approximately 4.5 to 6 V with respect to gnd. My DVM has a frequency measurement option, and so I had expected to be able to measure ‘something’ from the master (J519), on the assumption it would be continuously issuing commands on the bus. Unexpectedly (to me), my DVM measured 0HZ, so only DC was present. I am not sure if this is expected or if my DVM should have been reading the clocked messages, or would there be no clocked messages if no devices were on the bus? Im just not sure. I don’t believe there is anything else on this particular bus, as I don’t appear to have a G238 sender on my vehicle for example. Is there an idle DC voltage when all slaves are disconnected? I have reviewed the message format of Lin Bus with respect to command and response, but I’m not sure if the master keeps issuing messages hoping for a response eventually, with no slaves attached or if it goes into another state where only a reference DC signal is present, awaiting a slave to momentarily take it to gnd, as a heads up to the master to allow the master to then start issuing commands?!
I’m kind of at a brick wall and not sure what my next move should be. It appears that each of my 3 pins at the connector are doing what they are supposed to be (notwithstanding my uncertainty with pin 2 (Lin bus), so is my new OEM G395 which I bought from Audi last week, just defective?
Any other routes of enquiry would be greatly appreciated.
Thanks guys
I’m trying to diagnose the source of the fault that VCDS is complaining about regards my G395 pressure sender;
00256 - A/C Pressure/Temperature Sensor (G395)
What I have done to date:
I have replaced the part with another OEM. But fault persists and instantly annunciates its self following a clear of DTC through VCDS.
I have traced the cables back visually as best I could given the current flow diagrams. Could not test continuity with built in DVM buzzer; presumably because the impedance was too great on the Lin Bus. But visually I see no defects or issues from the G395 sender > A pillar coupling station > A pillar coupling station > J519 module.
With the sender disconnected, I have verified a healthy 14V supply at the wiring loom connector into the G395 sender, similarly the ground is also good.
I have no means to test the validity of the data coming from the 3rd a final core, I.e. the Lin Bus, but what I can say is there is no short to gnd. With the sender disconnected I am able to measure at the connector, a voltage which fluctuates from approximately 4.5 to 6 V with respect to gnd. My DVM has a frequency measurement option, and so I had expected to be able to measure ‘something’ from the master (J519), on the assumption it would be continuously issuing commands on the bus. Unexpectedly (to me), my DVM measured 0HZ, so only DC was present. I am not sure if this is expected or if my DVM should have been reading the clocked messages, or would there be no clocked messages if no devices were on the bus? Im just not sure. I don’t believe there is anything else on this particular bus, as I don’t appear to have a G238 sender on my vehicle for example. Is there an idle DC voltage when all slaves are disconnected? I have reviewed the message format of Lin Bus with respect to command and response, but I’m not sure if the master keeps issuing messages hoping for a response eventually, with no slaves attached or if it goes into another state where only a reference DC signal is present, awaiting a slave to momentarily take it to gnd, as a heads up to the master to allow the master to then start issuing commands?!
I’m kind of at a brick wall and not sure what my next move should be. It appears that each of my 3 pins at the connector are doing what they are supposed to be (notwithstanding my uncertainty with pin 2 (Lin bus), so is my new OEM G395 which I bought from Audi last week, just defective?
Any other routes of enquiry would be greatly appreciated.
Thanks guys