ABS - False Codes
TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERSDATE: April 1993
REF.NO. MBNA 42/12
SUBJECT:
MODELS 124 AND 201 WITH ENGINES 601, 602, 603
MODIFICATION OF HARNESS ROUTING TO PREGLOW TIME-LIMIT RELAY MODULE, CIRCUIT 30
In cases where the ABS warning lamp intermittently stays on after starting the engine, perform the complete ABS diagnostic test, as outlined in Service Information MBNA 42/6 (March 1990).
If no faults are found by testing, the problem may be caused by electromagnetic interference. The large current flowing through the preglow wiring harness can cause the ABS control module to recognize a fault during the self-test, where none exists. In this case, modify and reroute the preglow wiring harness as described in the Work Instruction 293, Group 42.
NOTE:
This repair procedure requires prior authorization from MBNA Regional Personnel.
Work Instruction
To eliminate intermittent complaints of the ABS malfunction indicator lamp remaining illuminated for several seconds after engine start, the harness routing to the preglow time-limit relay module circuit 30 must be modified according to the procedure described below. This should only be performed after performing a complete ABS diagnostic test.
Model 124:
1. Disconnect and cover battery negative terminal.
2. Disconnect circuit 30 wire from preglow time limit relay module (N14) (Figure 1).
3. Cut off ring terminal.
4. Disconnect circuit 30 wire from the preglow time-limit relay module (N14) at X4 (beneath rear of fusebox, in passenger compartment), cut off ring terminal (Figure 2).
CAUTION!
Make sure you cut the correct wire.
5. Insulate both wire ends and tape them to the harness.
6. Route a new wire (red, 6 sq.mm or 8 AWG stranded) from the relay module (N14) to X4/1O, located forward of the battery. It is very important that the new wire is routed exactly as shown. The new wire must be covered with plastic tubing (8.0 sq.mm) before installation.
7. From relay module (N14), route wire as follows: around relay module, along front of compartment wall, through compartment grommet (maximum distance from ABS wiring harness), along rear inside of wall towards center of engine compartment (Figure 3).
8. Continue alongside the starter wiring harness (through the compartment wall), across the engine compartment (Figure 4).
9. Proceed across the engine compartment with the starter wiring harness, then to the battery connector (X4/1O) (Figures 5 and 6).
10. install cable clips and ties as necessary or as shown.
11. Install and solder new ring terminals to the wire.
12. Connect to relay module (N14) and X4/1O.
13. Reconnect battery and test system.
14. Recode radio as necessary.
Model 201:
1. Disconnect and cover battery negative terminal.
2. Disconnect circuit 30 wire (4 sq.mm) from preglow time-limit relay module (N14) (Figure 7).
3. Cut of ring terminal.
4. Locate circuit 30 wire (4 sq.mm) for relay module (N14) at X4 location (beneath front fuse box). This wire is joined with a 6 sq.mm wire in a single ring terminal (Figure 8)
5. Cut the 4 sq.mm wire from the ring terminal. Be careful not to damage the 6 sq.mm wire.
CAUTION!
Make sure you cut the correct wire.
6. Insulate both wire ends and tape them to the harness.
7. Route a new wire (red, 6 sq.mm or 8 AWG stranded) from the relay module (N14) to X35 (same as X4/10), located forward of the battery. It is very important that the new wire is routed exactly as shown. The new wire must be covered with plastic tubing (8.0 sq.mm) before installation.
8. From relay, module (N14) route wire as follows: through compartment wall grommet (maximum distance from ABS wiring harness), along rear inside of wall to grommet above brake booster (Figure 9).
9. Route wire through grommet above brake booster, alongside the starter wiring harness, across the engine compartment (Figure 10).
10. Continue through the compartment wall with the starter wiring harness, then to the battery connector (X35 or X4/10) (Figure 11).
11 Install cable clips and ties as necessary or as shown.
12. Install and solder new ring terminals to the wire.
13. Connect to relay module (N14) and X4/10 or X35.
14. Reconnect battery and test system.
15. Recode radio as necessary.
Parts Information
In Case of Warranty