PRND432 all lit up part 2
01-03-2004, 12:36 PM
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some ideas.....
the following "external" links to/from the tcm are used:
from the tcm to the ecm:
1) the abs/asr -traction control means delaying shift points if the abs/asr system detects slip
2) motor intervention -triggers a slight reduction in power to make shifting smoother (this reduction is actually a reduction in torque gained by modifying injection timing)
from the ecm to the tcm:
1) engine load (g69) -throttle position sensor via the ecm (this is required for the dynamic shift program to work)
2) engine speed (g28) -this is required in order to work out the required shift pressure (smoother shifting).
3) fuel consumption -actual torque of the engine (used to calculate shift points). failure will cause the tcm to use the tps (g69) and rpm signals.
some thoughts.
1) torque reduction is used by the tranny to enable smoother shifting (should be clear from the above). this effect will be *less* in wet/slippery conditions as the abs/asr will delay the shift points. this is most likely the effect you describe in your point #1.
2) your point #2 puzzles me, as it seems in variance to your 1st point ie. your observation of higher shift points in the wet, yet also more agressive shifting? notwithstanding, from the above, there are 2 seperate control circuits from the tcm to ecm at work: the abs/asr one (it's wet and we'll delay shift points), and the motor intervention one (i'm about to change, reduce power).
actually, thinking more laterally, any one of these cause cause the effect you are describing.
3) i wonder if you have a bad throttle position sensor? if the value is bad, the tcm will use a substitute value, and will disable dss and force fixed shift points. worth checking this with vag-com.
4) the output speed (recorded off a sensor -g38- on the torsen) is used for the smooth shifting algorithm. the input speed (sensor g182) is used to calculate shift duration. this is compared to the tcm map. other paramters are, as you'd expect engine load and speed. these are not bad in your case, so we can rule them out, as failure will trigger the emergency mode.
in summary, i'd check the tranny fully 1st, before suspecting the tcm map. alternatively driving another a6 4.2q should clear up whether we talking symptoms of a problem, or reality.
hth...
from the tcm to the ecm:
1) the abs/asr -traction control means delaying shift points if the abs/asr system detects slip
2) motor intervention -triggers a slight reduction in power to make shifting smoother (this reduction is actually a reduction in torque gained by modifying injection timing)
from the ecm to the tcm:
1) engine load (g69) -throttle position sensor via the ecm (this is required for the dynamic shift program to work)
2) engine speed (g28) -this is required in order to work out the required shift pressure (smoother shifting).
3) fuel consumption -actual torque of the engine (used to calculate shift points). failure will cause the tcm to use the tps (g69) and rpm signals.
some thoughts.
1) torque reduction is used by the tranny to enable smoother shifting (should be clear from the above). this effect will be *less* in wet/slippery conditions as the abs/asr will delay the shift points. this is most likely the effect you describe in your point #1.
2) your point #2 puzzles me, as it seems in variance to your 1st point ie. your observation of higher shift points in the wet, yet also more agressive shifting? notwithstanding, from the above, there are 2 seperate control circuits from the tcm to ecm at work: the abs/asr one (it's wet and we'll delay shift points), and the motor intervention one (i'm about to change, reduce power).
actually, thinking more laterally, any one of these cause cause the effect you are describing.
3) i wonder if you have a bad throttle position sensor? if the value is bad, the tcm will use a substitute value, and will disable dss and force fixed shift points. worth checking this with vag-com.
4) the output speed (recorded off a sensor -g38- on the torsen) is used for the smooth shifting algorithm. the input speed (sensor g182) is used to calculate shift duration. this is compared to the tcm map. other paramters are, as you'd expect engine load and speed. these are not bad in your case, so we can rule them out, as failure will trigger the emergency mode.
in summary, i'd check the tranny fully 1st, before suspecting the tcm map. alternatively driving another a6 4.2q should clear up whether we talking symptoms of a problem, or reality.
hth...
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