I am desperately troubleshooting my 96 A4 2.8 quattro auto (not starting, no spark).

2 strange things that I can see:
a) RPM in VAGcom move when gas pedal is pressed
b) MIL/CEL light does NOT come when ignition is turned on

VAGcom shows only codes in
- auto trans: 1 Fault Found:
00526 - Brake Light Switch-F
27-00 - Implausible Signal
- auto HVAC: 4 Faults Found:
01297 - Sensor for Vent Temperature; Footwell (G192)
30-00 - Open or Short to Plus
01296 - Sensor for Vent Temperature; Center (G191)
30-00 - Open or Short to Plus
01206 - Signal for Duration of Ignition Off Time
27-10 - Implausible Signal - Intermittent
01582 - Signal for Coolant Temperature
30-00 - Open or Short to Plus
- airbags: 4 Faults Found:
65535 - Internal Control Module Memory Error
00-10 - - - Intermittent
00532 - Supply Voltage B+
07-10 - Signal too Low - Intermittent
00588 - Airbag Igniter; Driver Side (N95)
32-10 - Resistance too High - Intermittent
01025 - Trigger for On Board Diagnostic Lamp; Malfunction
31-10 - Open or Short to Ground - Intermittent

When turning the ignition on, the MIL (or CEL, not sure what the forum lingo is), doe NOT come on.

What can cause the light NOT to come on?

The usual 'no spark' culprits are (please correct, comment, add):
- crankshaft position sensor
- camschaft position sensor
- maybe speed sensor (sits on flexplate I think)

Before replacing sensors: would VAGcom show codes if they do NOT work properly?

What other 'no MIL check light' conditions can I check?

I am pretty much at the end of my wisdom after 10 days of checking/searching.

 

You've either got quite a few things wrong or you have some sort of bad connection, be it a ground connection or at the ECU or something. It seems suspicious that you have so many implausible signals.

 

Implausible signals in HVAC and Airbag; I wouldn't think they tell the ECU to "not spark" (and cause a NO CEL CHECKLIGHT).

Will VAGcom tell me if NO CEL CHECK is a the bulb are 'on purpose'?

If it matters: The current condition came after installing new/used transmission. Prior, motor was running fine (but no codes pulled). Battery was disconnected fro 2 weeks or so during removal and installation of new trans. Most of the messing around was under the car (shafts, shields, axles, transmission (2 wires I think), O2 sensors), some in the engine bay (driver side valve cover for access to exhaust flange and upper O2, water tank; passenger side air box/MAF, etc.) and front (replaced radiator).

 

You didn't crush any wires/hoses when installing the transmission? Perhaps the transmission came with some bad sensors? My point is that your scan is complaining about all of these wiring problems and it seems to me like the common link is probably either the wiring or some connector (or multiple connectors). Or ground.

 

You have a 96, which *I think* used bulbs in the cluster, could simply be that. Have you verified no spark?

 

The wires that are in the way are
- O2 sensors (checked, don't look bad)
- 2 wires with plugs from the trans

Some mentioned the trans shouldn't really do anything; should have spark no matter what.

Other wires in the area are:
- crank sensor (unplugged today, VAGcom shows error; plugged back in, no error; had sensor out and checked resistance: ok; metal object nearby creates change resistance)

- speed sensor (not taken out, but checked wire; seemed ok)

 

Yes, verified no spark.

After some more testing, the last log has NO engine or trans codes (only HVAC and airbags).

Also, I set VAGcom to reading groups but left everything alone, just set the last of the 3 rows to 'group 3' and click go. THEN, the RPM signal is NOT moving with gas pedal (stays at zero), just the "load" value goes up.
I VAGcom will see RPM when cranking in group 3?

When I click on Group 2 go and group 1 go, then funny things happen again.

 

Someone suggested the following, but won't explain how to do it (or what is really meant).

Can someone help me?

"You can check the MIL bulb with DVOM or with outputs in 17-03 go/next [VAGcom]

More then likely the following to be verified, a bad G28 [ground?], or in some MPI a bad ecu supply voltage relay [location?], or ignition switch [location?] during the crank circuit killing 15 [what is that and where? A fuse?]

DVOM will verify volts on G28 during crank regardless of ecu.

Check the key switch and supply relay first. [location? how to check?]

 

Get a digital multimeter (VOM = volt/ohm meter) and check whatever points are there.

 

You need to check power to the ECU as someone already mentioned, do this buy checking the supply power to the ECU and check to see if any of the engine management fuses are blown.