General Information

Volvo's microcomputer-based diagnostic system has two modes:
1) Self-diagnosis. Self-diagnosis means that individual electronics systems test themselves during use and store any faults for subsequent readout.
2) Test. Test mode is complementary to self-diagnosis, and is designed to assist in fault-tracing and checking the electronics system as a whole.

NOTE Test mode cannot identify which component is faulty (e.g. leads, actuators, sensors). This requires conventional fault-testing.

Diagnostic Connectors:

The DLC (Sometimes referred to as "Diagnostic Unit") is in the engine compartment, on the front of the control electronics box. There are two DLCs, A and B, with six terminals each. Manual readouts are possible via the DLC LED and push-buttons.





- DLC A has a LED, push-buttons and a selector cable with pins.
- Use DLC A7 to run manual diagnosis via push-buttons and LEDs for instrument panels with microprocessors (VDO).
- To retrieve DTCs from memory, read off LED flash sequences or use Volvo Scan Tool if available. Accessing Via Scan Tool (ST)

Manual Readouts Via DLC:

- Put selector cable pin in socket 7 on DLC A.
- Switch ignition on.
- Select mode by pressing button as shown below.

Selecting Test Modes:

- To select a test mode, press the button on DLC A the same number of times as the number of the test mode, e.g.: for DTM 5, press button five times.
- Further test modes use three digit codes consisting of numbers 0-9. E.g.: 1-5-1 to reset the service light (in DTM 4).
- Each digit is represented by pushing the button or the LED flashing that number of times, except for '0', which is represented by 10 flashes/pushes.
- Leave a pause between each digit.

Inputs:

For inputs, a pause is indicated by the LED coming on and staying on after a short while; for readouts, the LED stays off in the pauses between digits. When entering codes, press the button quickly and definitely (about 1 second).

Generally speaking, the procedure is as follows:
- Wait for LED to stay on, enter first digit of code.
- Wait for LED to stay on, enter second digit.
- Wait for LED to stay on, enter third digit.

There is one exception to this rule. When entering the mileage in a new VDO instrument panel, this has to be done in DTM 6. Do not enter a code, but the actual distance figure. For details of how to do this, DTM 6 (Entering Data)

Readouts:
Read off DTCs in store by counting the number of times the LED flashes. DTCs are read out in the order in which they were stored (FIFO, first in, first out). The system can hold up to 7 DTCs. If full, the system cancels the last DTC stored if its priority is lower than that of the new DTC.