navy721

Saved an Audi from the junk yard and I'm a little stuck.

The car drives is only in 2nd gear and reverse.

I scanned it and it can't find the TCM. The car came with disconnected TCMs. Vag Com can't read either of them.

I feel that that the Transmission Switch needs to be replaced. But I'm confused as to why the Vagcom can't read the TCM.

Ideas?

Thanks!

Prospeeder

Trans is in limp mode. Need to see if the trans computers are getting power and ground.

POWER SUPPLY
Switched voltage (Term. 15) is supplied to terminal 1 of the Transmission Control Module to power the TCM and unswitched battery voltage (Term. 30) is supplied to terminal 39 of the TCM to power the permanent fault memory. These power supplies are not fused.

SELF-DIAGNOSIS
After the engine starting sequence, if battery voltage goes below 9.0 volts, the transmission will go into Emergency Running Mode II.


PURPOSE
The Transmission Control Module (TCM) 01F/01K controls and monitors the operation of the automatic transmission. The TCM records any faults it detects and will go into "Fail Safe Mode" to insure operation and safety of the transmission if a critical fault occurs.

OPERATION
The TCM collects information from various sensors and other control modules such as the M.P.I. Engine Control Module (ECM) for engine management information and the ABS Control Module for information about road speed. After evaluating this information, the TCM generates output signals to the actuators.

The TCM also generates output signals to the M.P.I. ECM (to retard ignition timing during upshifts and downshifts) and the A/C Control Head (to switch off the A/C compressor clutch under full throttle acceleration.)

The TCM monitors all inputs and outputs to detect any faults or values that are outside of normal operating range. It is equipped with a permanent fault memory and self-diagnosis capabilities.

If the Transmission Control Module detects a critical fault, or the TCM fails, the transmission will go into one of two emergency running modes. The Emergency Running Mode level depends on the nature of the failure.

CONSTRUCTION

Two important relays are integrated in the Transmission Control Module:

• The Solenoid Valve Power Supply Relay
• Cruise Control Power Supply Relay The Solenoid Valve Power Supply Relay supplies voltage to shift solenoids N88, N89, N9O and ATF pressure modulating valve N91. The Cruise Control Power Supply Relay supplies voltage to the Cruise Control ON/OFF switch after the vehicle has reached a speed of 22 MPH.

Note :
Neither of these relays can be serviced. Should either relay malfunction, the TCM must be replaced. Both relays are checked during Output Check Diagnosis when using the V.A.G 1551.

<TABLE border=0 cellSpacing=0 cellPadding=0 width="100%"><TBODY><TR><TD vAlign=top align=middle><TABLE border=0 cellSpacing=5 cellPadding=0 width="90%"><TBODY><TR><TD bgColor=#336699 align=middle>Emergency Running Mode II</TD></TR><TR><TD align=right> </TD></TR></TBODY></TABLE></TD></TR><TR><TD vAlign=top align=middle><TABLE border=0 cellSpacing=10 cellPadding=0 width="90%"><TBODY><TR><TD>In this emergency running mode, the power to the Solenoid Valve Power Supply Relay in the TCM is cut off. This means the solenoid valves in the valve body will not operate and the transmission will not shift. Here's what happens if a fault develops while driving:

The transmission shifts to 4th gear. Since 4th gear is a direct mechanical connection between the engine and transmission, the engine will stall when the vehicle is brought to a stop.

After restarting, the transmission will operate in reverse (when selected) and in 2nd gear when you put the selector lever in D, 3, 2, or 1.


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