154e90
07-11-2021, 03:51 PM
Hello everyone,
This post is to document an experience I had that I did not find similar reports of on google. I hope it gives someone else with the same problem direction.
The car:
E91 335i converted 328i with a JB4, Alpina transmission tune, and other irrelevant performance modifications
N54 engine + ZF 6HP Auto
The issue:
After driving a few miles and stopping in a parking lot for a few minutes with AC on, I saw a transmission gear light appear in the cluster. It went away immediately, and then kept returning. I scanned the car at the time and there were no codes. It kept coming on and off repeatedly and dinging constantly, almost like a door chime. I started putting the car through all the gears to determine if it was a problem with a park neutral switch. It exhibited the same behavior in all gears. When I stuck the car in drive I could see on the display that it started out in 4th gear and slowly shifted back to 1st. (The Alpina tune shows forward gears in D, but I do not think the tune has anything to do with the problem. It just let me see what forward gear I was in.) The transmission was serviced with mechatronic sleeves and new fluid very recently, and it also had been performing perfectly. There was no hard shift when switching between gears and the light never returned when the car was in motion. I drove home without any further symptoms, issues, or lights. No more codes appeared upon my return to the house, but the car exhibited the same behavior.
The (incomplete) diagnosis:
I started to believe this was an input problem to the EGS and not something mechanical because I had absolutely no complaints about the transmission behavior or performance. I hooked up a scan tool and started to select data pids that would be inputs to the EGS not directly related to transmission operation. I selected temperature values, fluid pressures, and the vehicle speed, among other things in the EGS live data menu. The problem stood out immediately. The vehicle speed was fluctuating up to 6mph sitting still in all gears. I exited the EGS and started to look at ABS data to look at wheel speed inputs. My right rear wheel speed sensor was bouncing between 0 and 140 MPH. :nuts This was quite surprising given that there were absolutely no ABS codes and no brake pulsations. There is likely something wrong with the wheel speed sensor circuit.
Current status:
I drove the car once more after that day, and the car now has the ABS, BRAKE, and traction control lights on. The transmission light no longer appears. I suspect a bad wheel speed sensor, but I'll do a bypass test to ensure the circuit is fine before throwing one on the car. I may document that in video and post it here, or I may just return and post what ended up fixing this issue.
Wheel speed sensor is ordered and should be here on the 21st. I will have results shortly
I hope this helps someone.
This post is to document an experience I had that I did not find similar reports of on google. I hope it gives someone else with the same problem direction.
The car:
E91 335i converted 328i with a JB4, Alpina transmission tune, and other irrelevant performance modifications
N54 engine + ZF 6HP Auto
The issue:
After driving a few miles and stopping in a parking lot for a few minutes with AC on, I saw a transmission gear light appear in the cluster. It went away immediately, and then kept returning. I scanned the car at the time and there were no codes. It kept coming on and off repeatedly and dinging constantly, almost like a door chime. I started putting the car through all the gears to determine if it was a problem with a park neutral switch. It exhibited the same behavior in all gears. When I stuck the car in drive I could see on the display that it started out in 4th gear and slowly shifted back to 1st. (The Alpina tune shows forward gears in D, but I do not think the tune has anything to do with the problem. It just let me see what forward gear I was in.) The transmission was serviced with mechatronic sleeves and new fluid very recently, and it also had been performing perfectly. There was no hard shift when switching between gears and the light never returned when the car was in motion. I drove home without any further symptoms, issues, or lights. No more codes appeared upon my return to the house, but the car exhibited the same behavior.
The (incomplete) diagnosis:
I started to believe this was an input problem to the EGS and not something mechanical because I had absolutely no complaints about the transmission behavior or performance. I hooked up a scan tool and started to select data pids that would be inputs to the EGS not directly related to transmission operation. I selected temperature values, fluid pressures, and the vehicle speed, among other things in the EGS live data menu. The problem stood out immediately. The vehicle speed was fluctuating up to 6mph sitting still in all gears. I exited the EGS and started to look at ABS data to look at wheel speed inputs. My right rear wheel speed sensor was bouncing between 0 and 140 MPH. :nuts This was quite surprising given that there were absolutely no ABS codes and no brake pulsations. There is likely something wrong with the wheel speed sensor circuit.
Current status:
I drove the car once more after that day, and the car now has the ABS, BRAKE, and traction control lights on. The transmission light no longer appears. I suspect a bad wheel speed sensor, but I'll do a bypass test to ensure the circuit is fine before throwing one on the car. I may document that in video and post it here, or I may just return and post what ended up fixing this issue.
Wheel speed sensor is ordered and should be here on the 21st. I will have results shortly
I hope this helps someone.