case studies

This is a 2015 Nissan Versa. This vehicle came to me after the dealer told them it needed a transmission. Customer complaint was MIL and ABS illuminated with shifting concerns and brakes acting funny. His words not mine. Test drive confirmed the CVT trans was indeed acting like a slipping trans, high engine rpm and not much acceleration. The brakes were false activating ABS. Speedometer was acting up also. It would read then fall to zero and back to reading again. It was repeatable at the same speeds.

Scan for codes revealed several ECM codes. Sorry I don't have the code numbers anymore. This was two weeks ago. The codes were for output speed sensor erratic, VSS signal. The abs had 3 codes all for LF WSS. I was surprised to find no codes in the transmission controller. Scan data showed only ABS speed sensor problems at this time. No trans sensors showed a problem. I scoped the 3 speed sensors on the trans and found no problems.

I then scoped at the ABS connector on both front WSS pins. The capture I have attached is the fault I found. I noticed no repeatable pattern. It was very erratic. After a visual inspection of al the wiring I verified wiring integrity. No problems found. I decided the easiest next test was to swap the two front sensors. I checked for corrosion build up under the sensors. No rust. Simple to swap sensors on this one so I did. The problem was still there. It isn't a module misinterpreting the data as the scope showed the issue. Only one thing left. The trigger. Or the gap too big.

I was a bit hesitant here and had to think it through for a minute to be sure I had not missed something. I wasn't 100% confident that a wheel bearing would fix this as the pattern wasn't repeatable in the scope capture. It was repeatable at a certain speed. The trigger magnets for the sensor are built into the sealed bearing on this car. I pulled the trigger and sold a wheel bearing replacement. I found nothing in the bearing assembly that looked like a problem. The new bearing did in fact fix this car. The speedo worked correctly the trans shifted fine and the ABS no longer false activated.

The big surprise to me was the fact that one WSS on a car that has 4 and 3 shaft speed sensors on the trans would be so thrown off by 1 sensor acting up. Another example of testing and proving failures. I always try to fix what I know to be a problem before spending too much effort chasing the ones I can't find at the time. I waited till now to post this as I wanted the customer to drive it for a bit to make sure we didn't need more testing on other parts. He called and thanked me a thousand times for fixing it right and not doing what the dealer would have done.