Recently I was at an AAMCO shop in Hialeah, Florida. My friend Roger asked me to stop by and have a look at a 2016 Honda Accord he was having trouble with. It had a 2.4L engine and a BC5A transmission. According to Roger, the transmission would intermittently go into neutral when coming to a stop. The vehicle had been in an accident and was an insurance job. The accident damaged the transmission, so it was part of the claim, so the insurance company had a factory reman unit installed.
From the get-go, the transmission had this neutralizing problem, so the appraiser figured the transmission from the dealership was defective. After 34 days and three factory units with the same neutral complaint, they decided to diagnose the problem.
THE DIAGNOSTIC PROCESS
The BC5A transmission is a CVT, so it doesn’t have a low sprag. Therefore, the neutral complaint would be due to a slipping belt or clutch. Note: In the case of belt slippage, the computer initializes a torque management strategy to prevent catastrophic transmission failure. This hadn’t happened (not to mention three transmissions), so we began to look outside the unit. Hmmm.
We popped the hood and started looking around, hoping that something would be obvious, broken wire, or damaged something. At this point, we noticed that this vehicle was involved in a front-end collision with considerable damage.
It was at this moment when the light bulb went off! Do you remember the “Fuzzy Logic” these Honda’s have? Fuzzy logic is where the computer tries to understand what the driver is doing, and then it anticipates what might happen next. It uses the Automatic Braking System (ABS), Traction Control System (TCS), and the Vehicle Stability Control system (VSC) to know if the driver is going up a grade, around a turn, or some other maneuver. It’ll then control the transmission based on what it thinks the driver will do next, under those conditions.
Here’s where limitations come into play. Most aftermarket scan tools do not show in-depth data from these systems; you need a factory scanner for that. We asked the Honda dealership to scan and evaluate the PIDs from these systems. We were eager to see the results and BINGO! We got it!
All parameter readings were good in the ABS and TCS systems. The VSC, on the other hand, was not! This vehicle uses the VCS for a Hill-Start- Assist feature. Here’s how it works: It knows two things when the computer thinks the vehicle is on a grade. It knows that the driver has their foot on the brake, and at some point, they’ll go from the brake to the gas pedal. It’s during this maneuver that the car might begin rolling down the hill. To prevent this, it keeps the brake applied until it notices a TPS change. It may also disengage the forward clutch, depending on the condition.
The scan data from the VSC system showed the Lateral Sensor indicating a “rearward tilt” while the vehicle was on level ground. It has a “Neutral Position Memorization” procedure for re-setting the system, but it kept showing an “incorrect position message” on the scanner.
Knowing this vehicle was in an accident was enough to make us stop and rethink our plan. A closer look under the hood showed that the ABS module was dangling by one bolt and the wire harness. The technician added a bolt and a spacer to stabilize the ABS module (Figures 1 & 2). Now the computer recognized a level surface and let us go through the Neutral Position Memorization procedure, which includes manually adjusting the ABS module (Figure 3).
The ABS module responds to commands from the Traction Control System and the Vehicle Stability Control system. The VSC system is integral to the ABS module. Since the ABS module was bouncing around in the engine compartment, there were times where it landed in one position or another, making the issues intermittent. As a result, the strategies in play caused the VSC system to create an intermittent neutral condition.
This problem was a bit Fuzzy at the beginning. But, I had a great time with my friend Roger. Free lunch and a chance to revive old knowledge were well worth it in the end.
This might seem like a rare instance, but every manufacture uses similar systems. The next time you run into a “fuzzy” diagnostic problem, check for any indications of collision damage. You might just get a clear sign of an electronics problem that’s an easy fix. See y’all!
Editor’s Note: If you have J2534 hardware, you can purchase an online subscription to the Honda OEM website. This gives you full factory-level scan capabilities. It’s a great alternative to taking it to the dealer.