A Keen Perception of the Obvious
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 on
page 10). 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 on page 12). 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 NV 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
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. 
©2006 Transmission Digest