This condition may be caused by a malfunctioning check valve in the vacuum line (see Fig. 1) to the air pump switch-over valve. When the check valve malfunctions, vacuum flow to the diverter valve is restricted, preventing it from opening. Proceed as follows.

2.1. Test the secondary air injection function chain with SDS.

2.2. If the air pump can be activated with SDS but the function chain test fails, the vacuum flow between the air pump switchover valve and the diverter valve may be restricted, preventing the diverter valve from opening.

2.3. Check vacuum supply (see Fig. 2) at the diverter valve. If vacuum is < 500 mbar, change the check valve.

 

Parts Information

Mercedes-Benz Part Name                          Part Number

Secondary air injection pump                        Refer to EPC

Check valve                                                   A002 140 84 60

Secondary air injection pump relay
(M112, M113, M275, except AMG) (40A)   A002 542 72 19

Secondary air injection pump relay
(M271, M272, M273) (70A)                         A002 542 26 19 28

Secondary air injection pump relay
(M113K, M275LA AMG only)                     A002 542 66 19

Secondary air injection pump relay
(SLK320 and SLK32 AMG)                         A170 545 03 05

Secondary air injection pump relay
(C32 AMG and G55 AMG)                          A002 542 65 19

Note: When ordering a replacement relay, order the part number of the relay being removed. The parts system will deliver the current version of the ordered part.

Courtesy of ALLDATA.