Technically Speaking

• Subject: Problems caused by cross-connection of electronic components
• Units: R4A-EL, BAXA/MAXA, KM 175/77 (F4A series), VW 01M, AW 50-40, AX4S, R4A-EL, 4L60-E, RE4RO1A, A140
• Essential Reading: Rebuilder, Diagnostician, R & R
• Author: Wayne Colonna, ATSG, Technical Editor

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A no-move 1992 Mazda MPV van was towed into a shop, where it was determined that the planets inside the R4A-EL transmission were toasted. One look at the vehicle and you can see why (see Figure 1). This van recently had been involved in a front-end collision that collapsed the oil-cooler line, causing a lack of cooler flow, and there ya go – wasted planets.

So the shop rebuilt the transmission and installed an auxiliary cooler until the front end could be repaired, at which time the vehicle would receive a new radiator. Once the transmission was installed, it immediately went to failsafe.

The diagnostic connector on this vehicle is under the dash, left of the steering column (see Figure 2). The blue single-lead connector was grounded, and the Hold light (see Figure 3) flashed 60, 61, 62, 63 and 64 – every solenoid code available.

Well, this was obvious; there must be broken wires in the harness resulting from the front-end collision. As a technician traced the harness from the transmission, it seemed to travel directly across the damaged area (see Figure 4). But after half a day (10 a.m.-10 p.m.) of visually checking the harness as well as checking the wires for continuity, no damage was apparent. The solenoid resistance checked good at the transmission connector, yet when each solenoid’s resistance was checked from the TCM a definite problem was evident.

By this time, a new person was involved with the problem, and with a fresh mind and set of eyes, they discovered the problem. The inhibitor-switch and solenoid connectors were cross-connected, since their configurations are identical – something so simple, yet it took so much time and effort to discover.

An incorrect assumption as to the cause of the problem was certainly due to the front-end damage to the vehicle, and it was sensible, to say the least. But as shown by years of taking tech calls, mistakenly cross-connected connectors can be a time-consuming event to resolve even when there is no collision damage to mislead the technician. Here are the most-commonly cross-connected connectors we deal with on the tech lines so you can take note and avoid overlooking them in your shop:

1. 1998 Honda Accords with BAXA/MAXA transmissions. Complaints: Delayed engagements into reverse, harsh engagements into drive and bind-up on a 1-2 upshift. Cause: Connectors for shift solenoids B and C cross-connected with clutch-pressure-control solenoids A and B.
2. Mitsubishi KM 175/77 units (F4A series). Complaint: Aborts to third immediately or sometimes after the shift. Cause: Connectors for the pulse generators cross-connected with the shift solenoids. Earlier units would allow cross-connection of the pulse generator and the air-flow sensor.
   As an additional note, installing pulse generators A and B into the transmission incorrectly can result in either gear-ratio errors with an abort to third immediately after a shift or a condition in which Reverse will not engage from Park but will engage from Drive.
3. VW’s 01M transmission is similar to the KMs in that the transmission speed sensor and vehicle-speed sensor can be installed incorrectly, allowing a cross-connect of the vehicle harness. This usually causes a complaint of a 1-2-neutral shift. The vehicle-speed sensor is black and should go to the back of the transmission.
4. In Volvo and Daewoo vehicles with the AW 50-40 series transmission, cross-connecting the turbine-shaft-speed sensor with the vehicle-speed sensor causes a similar complaint as with the KM units when the pulse generators are installed incorrectly: No reverse from Park but will engage from the drive position. With Volvo vehicles, the speedometer also will be acting like an engine-speed gauge in the Park position.
5. Some 3.8-liter Ford passenger cars with the AX4S transmission have a short sub-harness for the vehicle-speed sensor that gets cross-connected with the rear heated oxygen sensor No. 2, causing harsh engagements and shifts. This cross-connection has been known to damage the computer.
6. AX4S can get the EPC solenoid cross-connected with the lockup solenoid should the internal wiring harness lose tie wraps. This causes a pulsating sensation.
7. Mazda 929 vehicles with the R4A-EL transmission can get the turbine-shaft-speed sensor cross-connected with a heated O2 sensor. This causes damage to the wiring harness as well as the computer.
8. In Kia Sportage and Sephia vehicles, cross-connecting the throttle-position sensor and the intake-air-temperature sensor causes a fixed TPS reading and extremely late shifts.
9. Bravada vehicles with a 4L60-E transmission and MV 136 transfer case can have the output-shaft-speed sensor and vehicle-speed sensor cross-connected, causing a bind-up feeling on takeoff.
10. In Subaru four-speeds with AWD, the locations of the two rear speed sensors (SSP 1 and 2) easily can be switched, causing an upshift into 4th gear by 20 mph.
11. The RE4RO1A in a Nissan Maxima can have the auxiliary air-control valve cross-connected with the inhibitor switch. Interesting enough, the vehicle will start but will make only a 1-2 upshift and the reverse lamps will not illuminate. This problem usually occurs after engine replacement.
12. Toyota four-cylinder passenger cars with the A140 transmission can have the internal wiring harness routed incorrectly past the valve body during installation, causing the two shift solenoids to be cross-connected. This causes a third-gear start with a shift to second, then a shift into first followed by a shift into fourth. Correcting this problem requires removing the valve body and routing the wiring harness correctly.

There are more cross-connect errors than those listed here, but these are the most common. This list no doubt will grow longer as the years go by, but it is a great heads-up to keep your eyes open looking for those cross-connect errors and prevent getting your wires crossed.

Now, I have to admit that I had one that just made me just shake my head in unbelief. It was a classic Toyota shift-solenoid cross-connect error that is No. 12 on the list. I explained to the technician how the two shift solenoids can be easily cross connected internally if the internal harness is routed incorrectly when the valve body is installed. Some have the internal harness that can disconnect from the case connector and then be reconnected incorrectly, causing the cross-connect. The technician said he was very confident that this was not the case, as he had many years of experience with this transmission. So the decision was made to shift the transmission with a shift box, and sure enough, it shifted fine. When the vehicle harness was plugged back onto the transmission the 3-2-1 (neutral) -4 shift returned.

This took us to the TCM, where it was discovered that this transmission must have been repaired once before and the internal harness apparently was routed incorrectly at that time, causing the solenoids to be cross-connected. Instead of dropping the pan and correcting the error, the shop that repaired the transmission previously decided to cut and swap the solenoid wires just a few inches from the TCM connector.

Now that this transmission had been repaired again but this time had the solenoids connected correctly, the technician had to correct the cross-connect in the external harness to resolve the problem.

Will this happen again? Who knows? Anything is possible, and it proves that you need to have more than a keen perception for the obvious.