M-Class (W163) Produced 1998-2005: ML 230, ML 320, ML 350, ML 400 CDI, ML 430, ML 500, ML 270 CDI

1998 ML320 crank no start. Ignition switch or AAM?

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Old Jan 14, 2026 | 08:31 PM
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From: Thousand Oaks, CA
1998 ML320
1998 ML320 crank no start. Ignition switch or AAM?

Hi all I am experiencing an issue with my 98 where as of a few days ago, I can not get it started. Initially I though it had something to do with the intake manifold vacuum leak repair leak I had done right before it, however after double checking all my work I am led to believe this is a random and separate issue. At first the car would start, fire a few times, and die so I suspected a bad crank position sensor or timing position sensor, both of which I replaced with Bosch units. I also trickle charged the battery since the car had been sitting for a bit. Still no start and now it doesn't fire either, just cranks for the 5 seconds. Now running out of ideas I decided to replace the battery since it was older and seemed like it was on its last legs, cleaned all the injector and coil pack electrical plugs, unplugged the MAF sensor and let the AAM sit disconnected from power overnight. No dice. I checked power to the fuel pump and found that the main supply terminals were 12v, however with the key in position 2, the switch terminals (which I assume are controlled by the AAM) read only 8v constantly, falling to 6v during cranking which is not enough to trigger the relay. This seems odd to me since I may be wrong but I though the pump was supposed to prime for a second in position 2 and run during cranking. Hard for me to know for sure now since it wont do anything. I jumped the fuel pump relay and it sounds like the pump runs strong (although I have yet to test pressure at the rail) and the pump is only about 3 years old since its replacement, filter/pressure regulator only a year old. At this point I'm starting to worry this is an AAM issue, even though I see no start error message on the display, the remote behaves normally, and the immobilizer LED on the dash blinks once every 3 seconds with any of my keys in position 1. Why would the fuel pump not be activated during cranking? Is a constant 8v through the switch normal? I'm not sure if this is an AAM issue or a ignition switch issue. Could an ignition switch be responsible for only the fuel pump not turning on? I have yet to test if other components like the injectors or coils aren't receiving power during cranking as well. If it is an AAM issue, can i get the keys reprogrammed with new chips or do I need to send off the AAM to be repaired with new keys as well? Any input would be greatly appreciated.
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