This topic is for a EXV2 model built in 2013.

While driving in forward or reverse the drive wheels will momentarily lock up and release, sometimes several times rapidly. This has occurred at low speeds and full speed. No errors in the BMS but after this happens a few times the motor controller will show errors 51 & 36 (CAN communication error & LOS/encoder error) . Ignition cycle clears the errors. I've checked continuity and connections for all CANBUS wiring and replaced the B&B CAN isolator with no change. I inspected the motor encoder and it is mounted solidly, the wiring is intact going back to the controller. I was able to connect my Fluke to the encoder A output and watch the frequency change as I changed speed like I expect. Are there other tests I can perform to narrow down this issue?

 

 

You are experiencing two separate issues. 

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Error code 36 is an encoder issue and is what is causing the erratic operation. It can also throw error code 73. Both are caused by the same issue. Basically, the speed controller is losing the encoder signal. Encoders can fail in a way that they work until a specific speed. So, testing with a meter can be difficult. I would recommend checking the wires from the encoder. If all looks good, then take in replace the encoder. Encoder part# U2601A-1N. If wiring is questionable U2601A-3N. Cycling key would remove this code.

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Error code 51 is another issue that does need to be resolved. Anytime the controller losses CANBUS signal will issue this code, and key does need to be cycled to remove code. When 51 is issued the vehicles top speed in forward is reduced to 5 MPH. The controller needs this CANBUS signal from the BMS to know how many amps it can draw from the lithium battery pack. The CANBUS isolator does have two lights on it. In normal operation both these lights should be flickering very fast. The fast flickering will make the lights look dim. If this is the case, then you would just have a connection issue between the isolator and the speed controller. If either of both lights are on solid, they will look bright. This would mean the CANBUS signal is locking up typically caused by a bad isolator, bad component connected to the CANBUS or the high and low wires of the CANBUS are touching each other. 

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In this model of vehicles, it was more common to see and encoder being bad. So, my best guess is the encoder itself is causing code 36. Also, the wiring to the isolator can be loose or touching each other right at the connectors going to the isolator. I would check over this wiring. So, I would start by replacing encoder and checking this wiring.      

 

 

Thank you for your time. After writing you about my problem I went back through the encoder wiring. I unplugged and reconnected the plug approximately 18 inches from the encoder pickup and my stutter and encoder error have gone away. It seems that the pins in the plug had gotten a bit corroded and was getting worse over time. I haven't had the error 51 come back since posting. The truck is driving great now, thank you so much.