09 Lincoln MKX No crank, No start, No Communication
As a mobile Tech I think I see some weird cars. The longer I do this the less weird they seem. I am a Mobile tech/programmer in the metro Detroit Area. I am teaching my son to do some drive ability diagnosis. He is currently a programmer. I have had him do many basic tests in the past and usually trust what he tells me. I say usually because I didn't trust him on this one and now I feel kind of bad about it. The victim of today's case study is at a shop that I do a fair amount of diagnostics work for. They know their limitations and do not put parts on without discussing with me. They have installed a used PCM and I am called to program it. I ask about the 2 keys etc, I typically do not inquire of why they are replacing component that needs programming. So I send my son to the shop to program the PCM. It is a NO COMM. I ask if they want it diagnosed and he says yes. OK lets get some basics done and maybe save me a trip. I ask him to plug BOB in and measure 6 and 14 ohms. key has been off for about 5 minutes. diag.net/file/f3nylfjls…
he says 93 Ohms, I said WHAT? no way. Unplug PCM diag.net/file/f5lww3m4c…
169 ohms, Ok obviously you are doing something wrong. I had him check powers and grounds at PCM and discovered were missing Run/Crank relay power and the fuse box was melted. He said looks like someone stuck a screwdriver in it. I called and explained to shop to get a fuse box and likely I would have to schedule to return. Start with the obvious.
Return visit: I start with the fuse box and make sure that the power that was missing has been restored and it was. I then grab my BOB and check the resistance across 6 and 14 and am amazed when the numbers are just as my son said. So I grab my IDS and decide next step has to be a network test.
As you can see I have the entire HS CAN bus down:
What is the strategy NOW? They have multiple Junction blocks, I make a decision based purely on instinct or Gut or whatever you want to call it. Lately I have had about 10 airbag modules causing all kinds of weird problems. So yup I went for it. I disconnected the Airbag module and instantly I heard the fuel pump run and the theft light was no longer flashing. The owner of the vehicle will be contacted about a RCM replacement. I am sure they will decline further repairs as my diagnosis likely was more than should have been spent on this car. It is a POS. to say the least.
Hopefully the information provided can help someone in the future. I did not remeasure 6 and 14 after disconnecting airbag module.
Every car I see is weird AND a POS, Sam, and I'm not even mobile. I do get to live in the tropics though. :-) Thank you for sharing, Aloha.
I would be curious to see the scope pattern of the network when the system was acting up. It is strange how frequently RCM's are the culprit of HS can faults for Fords. I have seen this as well.
Thanks for sharing Sam, enjoyed reading the case study. Thankfully you’ve had prior experience wother failed RCM’s
Thanks Sam, I appreciate the time and effort. If this your goto BOB for obd?
I also have the AES wave and the OTC and an old BOSCH one. I don't really have a favorite, They are all unique. The OBD aid I used to carry. I now sell and support the AES wave one.