Reading Diagnostic Trouble Codes

Typical Fault Indicator Light:

Audi vehicles with the MPI system, are equipped with a fault indicator lamp, and have a permanent fault memory. The fault lamp will illuminate when a problem is detected. If the problem is intermittent, the light may go out when the fault is no longer present, or may stay on until the memory is cleared (depending on the particular software in the computer). Emission related trouble codes will remain in the computer memory until manually erased, or, if the fault disappears and does not recur for 50 engine starts, it will be erased automatically. Other non-emission related codes are stored in a volatile memory and cleared each time the engine is started, or in some cases, when the ignition is turned "off".

Under Dash Diagnostic Connectors:

Vehicles equipped with the MPI engine management system have special test connectors for activating and reading fault codes. Early 1990 models (produced before March 1990) have two connectors, while later models (produced after March 1990) have three. These connectors are color coded for identification and are located below the dash panel, on the driver's side. Vehicles equipped with this system do not display codes through the fault indicator lamp. Instead, an LED test light must be connected between the test connectors to display codes. Models with these new connectors may still use a fuel pump relay with a fuse receptacle on top. Inserting a fuse into the relay will cause the fault indicator lamp to illuminate and stay on until the fuse is removed, however, this is a fuse and bulb check only. The fault memory display cannot be activated through the fuel pump relay.

ACTIVATING FAULT MEMORY DISPLAY

1. Make sure all fuses are OK, and operate vehicle for at least 5 minutes, being sure that engine speed excedes 3,000 rpm at least once and throttle is opened to wide open throttle position at least once ("punch it" once during test drive), then let engine idle for an additional 2 minutes. Do not turn engine off as some models will erase the temporary fault memory when the ignition is turned off.

a. If the engine won't start, make sure all fuses are OK, and use the ignition key in the start position to crank it over for at least 6 seconds. This will allow the ECU to read signals from input sensor, check for incorrect readings, and restore or set fault codes (if any). Don't turn ignition off, fault memory may be erased.

Diagnostic Connectors - Activating Self Diagnostics:

2a. (Models produced up to March 1990)
With engine running (or key "on"), connect LED test light positive lead to top terminal of black connector, and negative lead to bottom terminal of brown connector, using appropriate flat male connectors. Also, connect one end of a jumper wire to the bottom terminal of the black connector, and leave the other end free.

Diagnostic Connectors - Activating Self Diagnostics:

2b. (Models produced from March 1990)
With engine running (or key "on"), connect LED test light positive lead to top terminal of black connector, and negative lead to top terminal of blue connector using appropriate flat male connectors (the third connector, shown as a white connector in the diagram, is a blue connector on this model). Also, connect one end of a jumper wire to the bottom terminal of the black connector, and leave the other end free.

If you are not sure which lead on your test light is the positive lead, connect test light between the battery terminals. If the LED lights up, you have the positive lead on the positive terminal. If not, reverse the connections. If it still doesn't light, get a new test light.

3. Touch the free end of the jumper wire to the bottom terminal of the brown connector for at least 4 seconds, then remove. Fault memory is now activated.

4. Observe LED. A start up code will display (light on once for 2.5 seconds then off for 2.5 seconds) followed by the first code stored in memory.

5. After the first code is displayed and recorded, touch the free end of the jumper wire to the bottom terminal of the brown connector again for 4 seconds then remove, to retrieve the next code. This step must be repeated for each code until ending code 0000 is displayed, indicating all stored codes have been displayed. Code 0000 is represented by the light coming on for 2.5 seconds at regular 2.5 second intervals. Record all codes as they are displayed.

6. Turn ignition "off". Remove jumper wire and test light.

READING FAULT CODES

When the fault memory display is activated, the ECU will display a start signal, and then the first code, by flashing the properly connected LED test light. Codes are four digits long and are read by counting the number of flashes in each sequence.

Reading Fault Codes With LED Test Light:

After one sequence of flashes is displayed, designating one code, that sequence will repeat until the next sequence is manually activated. For example, 2 flashes-short pause, then 1 flash-short pause, then 4 flashes-short pause, then 2 flashes-long pause, repeat, indicates a code 2142 (no signal from knock sensor #1). The next code will not display until activated in the same way as the first. All codes are read in the same manner except for code 0000 (end of display) which is displayed by the light staying on for 2.5 seconds, then going out for 2.5 seconds alternately.