Issue Summary:
- A damaged bridge seal can result in pressure loss, causing a ZF 6HP26 in a 2002 BMW 745Li to be stuck in park.
- After overhaul, a Honda vehicle with an MGHA-family transmission exhibits wrong-gear starts, and various solenoid DTCs may be stored.
- Some 2002 Mazda MPVs can have harsh shifts with the MIL illuminated and/or the OD light flashing, and no DTCs stored.
- Engine speed in a 2006 Honda Civic with a CVT sometimes stays around 4,000 rpm during deceleration as the vehicle is being driven straight ahead.
A 2002 BMW 745Li arrived at the shop on a tow truck. When the vehicle was started, the steering-wheel paddle-shift controls were operated to select drive. The technician observed the gearshift-position indicator lamps go from park to neutral to drive and then immediately return to park.
The rubber “bridge seal” that goes between the Mechatronic (valve body) assembly and the pump had blown out (Figure 1).
With the bridge seal being damaged, a significant loss of system pressure occurred; this caused insufficient clutch pressure resulting in slippage. The TCM recognized this as the input-speed sensor maintaining a reading when it should have been zero rpm while in gear with the brakes applied.
At this time the TCM commanded the transmission back into park in an effort to prevent any further transmission damage.
Replace the bridge seal. BMW vehicles equipped with “shift by wire” are controlled by an “E”-type valve body referred to as a “Mechatronic Module.” The alternative is an “M”-type valve body, which has a conventional manual valve and gear-selector lever. The “E” type does not have a manual valve; it has a rod that is actuated by solenoids and moves the internal linkage to engage and disengage park and other gear selections. A preloaded barrel spring mounted on a rotating lever operates the park rod, with the tension of the spring pushing the lever and rod into the park position. To release park, the MV3 and MV2 solenoids are energized (Figure 2).
Figure 3 shows the park rod and the locations of the MV2 and MV3 solenoids.
The MV3 solenoid is mounted on the back side of the park-lock cylinder, which is on the valve body. Inside the cylinder there is a piston that connects to the rotating lever. When the MV3 solenoid is off, a shaft extends out from the solenoid, pushing the rear of the piston and lever into the park position. When a command is received to release park, the MV3 solenoid is energized and the shaft retracts. At this time the MV2 solenoid also is energized and supplies fluid pressure to a chamber inside the front area of the cylinder, pushing the piston, rotating lever and park rod into the released position.
Figure 4 shows one example of the garage shift-by-wire controls. This is the shift lever that signals the computer for gear selection. The selector lever operates as follows:
Position R: To select reverse the driver must have the foot brake applied and the selector lever pushed up to the end of its travel.
Position N: If the neutral position is desired while the transmission is in reverse, a downward tap on the selector lever is all that is needed. From the drive position, an upward tap on the selector lever is all that is required. From the park position, a tap on the lever in either direction will place the vehicle in neutral. Neutral will automatically be selected when the ignition is turned off but the key remains in the cylinder. Park will automatically be selected after 30 minutes unless N is selected before 30 minutes has elapsed, at which time an additional 30 minutes is added to the time in neutral.
Position D: Depress the foot brake and pull the selector lever to its fullest travel downward.
Position P: Park engages by a push of a button built into the selector lever. Park automatically disengages when R, N or D is selected with the engine running. Park will automatically engage when the ignition key is removed from the cylinder.
The instrument cluster shown in Figure 5 displays the results of selector-lever operation.
Some vehicles will have the selector lever and steering-wheel-mounted paddles as shown in Figure 6.
There are many safety features related to this system, such as a message display center in the instrument cluster informing the driver of a problem.
Should the vehicle get stuck in park and need to be moved, there is an emergency park-release lever under the dash. The handle is behind a locked access panel. The ignition key will unlock this access panel to reveal the handle, which is connected to a cable that when pulled or pushed will mechanically release or engage park.
- Bridge seal . . . . . . . . . . . . . . . ZF part number 0501215718
After overhaul, a Honda vehicle equipped with an MGHA-family transmission exhibits a complaint of wrong-gear starts. When checking for codes with a scan tool, you may find various solenoid DTCs stored.
One cause may be cross-connection of solenoid connectors. Cross-connecting the brown or black connectors among shift solenoids A, B and C and the TCC solenoid may cause wrong-gear starts but would not set DTCs. Cross-connecting black or brown connectors of shift solenoid A, B or C or the TCC solenoid with CPC solenoid A, B or C also may cause wrong-gear starts and most likely will store a DTC for the affected solenoids.
Use the diagram in Figure 7 to identify the proper solenoid locations.
There are a few different brown and black connectors. Use the chart in Figure 8 to identify the correct solenoid-connector color and corresponding wire color to assist the technician in correct assembly.
Note: Wire colors provided are based on the 2001-model Acura MDX. Use care when connecting the solenoids. Wire colors may vary between models; however, connector colors remain the same.
Some 2002 Mazda MPV vehicles may exhibit a complaint of harsh shifts with the MIL illuminated and/or OD light flashing. Code retrieval with a scan tool indicates no DTCs stored.
One cause may be a problem with the transmission control module (TCM). When you check for DTCs on these vehicles, the scan tool will indicate no codes. A Mazda technical-service bulletin (TSB 05-011/02) concerning this problem says the TCM needs to be re-flashed to make retrieval of DTCs possible. If the problem remains after the re-flash has been performed, the next step is to replace the TCM.
Replace the TCM.
The TCM on the 2002 Mazda MPV is on the passenger-side flooring just below the glove compartment and is bolted to the PCM bracket.
When a 2006 Honda Civic Hybrid with continuously variable transmission is decelerating from highway speeds while being driven straight ahead, the engine speed occasionally stays around 4,000 rpm.
This vehicle is equipped with a “Corner G Control System.” While the vehicle is decelerating through a corner, this system changes the transmission pulley ratios to obtain the best engine speed.
If there is even a minor difference in size between the rear tires, the PCM may “think” the vehicle is turning into a corner when it is not. This causes higher-than-normal engine speed during deceleration during straight-ahead driving.
The number of revolutions per mile can vary between tires of the same nominal size but from different manufacturers, resulting in the complaint mentioned.
Reprogram the PCM with HDS Software Version 2.010.003 or later to give the PCM greater tolerance to small size variations between tires.
- Updated program ID . . . . . . . . . . . . . . . . . MXA550
- Revision part number . . . . . . . . . . . . . 37806-RMX-A55
April 2009 Issue
Volume 26, No. 4
- BMW ZF 6HP26: Stuck in Park
- Honda/Acura MGHA Family: Wrong-gear starts; various solenoid codes set
- Mazda MPV JF506E, 2002 only: Harsh shifts; MIL on/OD light flashing; no DTCs stored
- Honda Civic Hybrid: High engine speed on deceleration