Recently a Honda Accord Crosstour was towed in with two seemingly unrelated problems. The first problem was that the charging system light had come on and the car wouldn’t start. The second was it wouldn’t go into reverse. I hooked up a jump box and started it, and confirmed that the charging system light was on and it wouldn’t go into reverse. I pushed it out of its parking spot and put it in drive, which did work, and made it into the shop before the jump box I was running the car with ran out of power.
I attempted to charge the battery, but my charger just flashed the error light, and then the shop’s battery tester just kept saying to hook it to a battery, so used my multimeter to find that the battery had a grand total of 0.15 volts out of the 12.6 it should have. Clearly the alternator had gone bad and running the car without it had completely killed the battery. Without being able to run the car, I couldn’t even try to diagnose the transmission issue, so I started out by selling an alternator and battery. After installing them, the car would now go into reverse. I’ve never experienced low system voltage causing a transmission to not function, but now I know that it can. The internals of a transmission are all controlled by fluid pressure, but changing where the fluid flows is often controlled with electrical solenoids, so it is possible that without an alternator and running on low battery voltage that there wouldn’t be enough power to engage the required solenoids.
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