See Figures 1, 2 and 3
- Open diagnostic socket cover and install selector cable into socket No. 2 for fuel injection codes or socket No. 6 (except Motronic systems) for ignition codes.
- Turn the ignition switch to the ON position.
- Enter control system 1 by pressing the button once. Hold the button for at least 1 second, but not more than 3.
- Watch the diode light and count the number of flashes in the 3 flash series indicating a fault code. The flash series are separated by 3 second intervals. Note fault codes.
1f there are no fault codes in the diagnostic unit, the diode will flash 1-1-1 and the fuel system is operating correctly.
If diode light does not flash when button is pressed, or no code is flashed there is a problem with the soft-diagnostic system, proceed as follows:
- Check ground connections on the intake manifold, and the ground connection for the Lambda-sond at the right front mudguard.
- Check the fuses for the pump relay and the primary pump. On 240 models, fuses are located inside the engine compartment on the left side wheel well housing. On 760/780 models, fuses are located in the center console, just below the radio. On 740/940 models, fuses are located behind the ashtray. Access can be gained by removing the ashtray, and pressing upward on the tab marked electrical fuses press. On 850 models, the fuses are located on the left side of the engine compartment behind the strut mount plate. The fuses on 960 models are located on the far left side of the dashboard. The driver's door must be open to gain access to the fuses.
- Remove glove compartment, and check control unit ground connections.
- Turn the ignition switch to the OFF position. Remove control unit connector and connector protective sleeve.
- Check diagnostic socket by connecting a voltmeter between ground and No. 4 connection on the control unit connector. Reading should be 12 volts. If no voltage is present, check lead between control unit connector and fuse No. 1 in the fuse/relay box.
- Turn the ignition to the ON position, and install selector cable into the No. 2 socket on the diagnostic socket. Connect a voltmeter between ground and No. 12 connection on the control unit connector. Reading should be 12 volts. Press the button on diagnostic socket and note reading. Reading on the voltmeter should be 0 volts. If no voltage at the control unit is present, take reading at the diagnostic socket connector. If reading remains at 12 volts when button is pressed, check diagnostic socket.
- Connect a voltmeter between ground and the red/black lead on the diagnostic socket connector. Reading should be 12 volts.
- Connect a suitable ohmmeter between ground and the brown/black lead in the diagnostic socket connector. Reading should be 0 ohms.
- Turn the ignition to the OFF position. Connect ohmmeter between diagnostic socket selector cable and the pin under selector button. The ohmmeter should read infinity. Press the button and note the reading. The reading should be 0 ohms.
- Connect a suitable diode/multimeter tester, or equivalent, between the diagnostic socket diode light and the selector cable. Connect red test pin from the tester to pin under diode light and black test pin from tester to selector cable. A reading on the tester indicates correct diode light function. With no reading on tester, replace diagnostic socket.
- Check the system relay/primary relay by connecting a voltmeter between ground and the No. 9 connection on the control unit connector, then connect a jumper wire between ground and No. 21 connection on the control unit connector. The relay should activate and the reading should be 12 volts.
- Press the diagnostic socket button. Note any additional fault codes.
The diagnostic system memory is full when it contains 3 fault codes. Until those codes are corrected and the memory erased, the system cannot give information on any other problems.
- Press the diagnostic socket button for the third time to see if a third fault code is stored in the memory. If the diode light flashes the same code 1-1-1, there are no other codes in the memory.
See Figures 4 through 15
Reading the control module memory is on of the first steps in OBD-II system diagnostics. This step should be initially performed to determine the general nature of the fault. Subsequent readings will determine if the fault has been cleared.
Reading codes can be performed by any of the methods below:
To read the fault codes, connect the scan tool or tester according to the manufacturers instructions. Follow the manufacturers specified procedure for reading the codes.