Timeline for Shorted battery on 2020 Mercedes A35, now car won't start
Current License: CC BY-SA 4.0
20 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Dec 30, 2023 at 5:58 | comment | added | Pedram | I also found out that the high pitched buzz is coming from the transmission oil pan. I think the pump is trying to run because the oil was low at one point. I put more oil in, but since I can't start the car, I can't run the procedure to check the oil level with a scanner. | |
| Dec 30, 2023 at 5:56 | comment | added | Pedram | Hi Howie. I got the shop manual that has wiring diagrams. How do you think that would help? One other thing I did is put a wire to the starter relay and the starter cranked, so I confirmed that the starter is OK. The car wouldn't start though even though the starter was cranking. I also pulled out the aux. battery and it was totally drained. I charged it back to full and stuck it back in but still no dice with the car starting. | |
| Dec 20, 2023 at 19:10 | comment | added | Pedram | I don't unfortunately, but I have one on the way. It's being shipped from overseas so I'm not sure when it'll arrive. I've also heard a parasitic drain and high pitched sound could be an issue with the alternator. With the car not starting I'm not sure how to test the alternator though. | |
| Dec 20, 2023 at 15:40 | comment | added | HandyHowie | Have you got a wiring diagram for the vehicle? | |
| Dec 20, 2023 at 5:47 | comment | added | Pedram | One other thing I noticed is that the battery gets drained when it's connected but the car is off. I'm hearing a high pitched whine when I plug the battery back in. I can't get where it's coming from but it seems like it's deeper within the engine bay. Could there be a blown relay in there somewhere that's causing that? I do hear a click when trying to start the car, so it seems like the car is sending the signal to start, but I'm not sure if it reaches the starter motor. | |
| Dec 20, 2023 at 5:45 | comment | added | Pedram | there are a whole bunch of codes that came back. many relate to currently unplugged parts, but there are a bunch that start with U (e.g. U010000) that relate to communication. The one about losing communication with the ECU didn't come back though, which is a good sign. Maybe that means it's communicating with the ECU now. | |
| Dec 17, 2023 at 22:26 | comment | added | HandyHowie | I would clear all of the codes, then see which ones come back. Those will be the important ones. | |
| Dec 17, 2023 at 22:11 | comment | added | Pedram | it could also be because I unplugged the ECU at one point | |
| Dec 17, 2023 at 20:53 | comment | added | Pedram | I got a whole bunch of codes because there are many parts that are currently disconnected, but one code that seems to relate to the ECU is U0100 "Lost communication with ECM/PCM". Would that happen with ECU damage? | |
| Dec 14, 2023 at 9:39 | comment | added | HandyHowie | If the ECU is damaged, then you will likely get no response from it. | |
| Dec 14, 2023 at 1:07 | comment | added | Pedram | I'm going to borrow a friend's Autel diagnostic reader this weekend and try reading whatever code there is then. I should have a better idea at that point. | |
| Dec 13, 2023 at 23:05 | comment | added | HandyHowie | Have you tried connecting an OBD2 reader? It would be interesting to see if it did anything. | |
| Dec 13, 2023 at 23:00 | comment | added | Pedram | OK thanks for the response. I'll take it to an ECU repair shop to have them check it out. | |
| Dec 13, 2023 at 22:36 | comment | added | HandyHowie | You want everything off to do the test. I believe the fact that there was initially no continuity backs up my theory that there is damage in the ECU. It may be repairable, but it is also possible that major damage has been done. | |
| Dec 13, 2023 at 20:57 | comment | added | Pedram | I went back to check the resistance and it wasn't registering continuity any more, which I thought was odd. I then put the car in accessory mode and then turned it off, and it started registering continuity between the negative terminal and the ECU. When in continuity mode, the number on the display was -489. I put it in resistance mode (Ω) 20 and the number on the display was -12.1. I hope that answers your question. | |
| Dec 13, 2023 at 8:31 | comment | added | HandyHowie | Just to confirm, with the case of the ECU not touching the bodywork at all, you have a very low resistance between the case and the battery negative terminal? Do you recall how many ohms? | |
| Dec 13, 2023 at 6:59 | comment | added | Pedram | I checked and yes, with the battery terminals connected there is. | |
| Dec 12, 2023 at 23:36 | comment | added | HandyHowie | Have you checked continuity between the ECU case and the battery negative terminal? | |
| Dec 12, 2023 at 23:34 | comment | added | Pedram | OK so I unplugged the ECU and the dash still comes on line before, so it looks like that stuff doesn't need the ECU. Should I check the wires coming to the ECU now to see if they got burned by the current going through them? | |
| Dec 12, 2023 at 19:59 | history | answered | HandyHowie | CC BY-SA 4.0 |