bamabob

My auto tranny has been acting up for quite a while now. More of a annoyance than anything else. Took it to the dealer and they found a code P0734 'A/T 4th gear signal repair'. They basically said do a tranny flush and if that's not it, a VB replacement will be needed - ouch! Anyway, does a VB mod like Don's correct a faulty running VB or he is simply tweaking a good one?

Daniel B. Martin

See Don's Web site at http://www.mobiletek.net/vb.html . Inquire by E-mail to info@mobiletek.net .

I believe he tweaks a good Valve Body. If your VB is misbehaving because of a bad solenoid you will have to fix that yourself... or possibly pay Don an additional fee to have him do it.

Sonic

The solenoids are attached to a wiring harness that goes into the engine bay, the VB (sitting in the transmission) will not fix the solenioids. Did he state a new solenoid harness or a VB change?

Daniel B. Martin

This information comes from the '99 Maxima factory service manual.

You can do some troubleshooting without removing the automatic transmission valve body. Find the harnesses which emanate from the transaxle. One of them terminates in a brown plastic connector with eight pins. This is connector F42, and is located (approximately) above the transaxle case and below the black plastic engine air intake ductwork. With the engine off, disconnect F42. You want to measure the transmission side of F42. Hold the connector such that the plastic latch is at the top. You should now see two rows of four terminals. These are numbered (top row, left to right) 1 - 4, and (bottom row, left to right) 5 - 8. Make resistance measurements between a clean ground and the following terminals:
#1, Shift solenoid B, 20 - 40 ohms.
#2, Shift solenoid A, 20 - 40 ohms.
#3, Overrun clutch solenoid valve, 20 - 40 ohms.
#4, Line pressure solenoid valve, 2.5 - 5 ohms.
#5, Torque converter clutch solenoid valve, 10 - 20 ohms.

There is also a "bench test" procedure for testing these solenoids with a 12 volt supply such as a car battery. However, this requires removal of the shift solenoid valve assembly. I don't know if you want to get involved with that.

The ATF temperature sensor resistance is measured across terminals #6 and #7 of F42.
At 68 degrees F, the resistance should be approximately 2.5Kohms.
At 176 degrees F, the resistance should be approximately 0.3Kohms
A defective ATFTS could prevent the transmission from shifting into 4th gear.

bamabob

The service invoice states "Needs flush first. If flush does not rectify will need valve body replaced." I will try what DBM has posted. I have been driving with this for about 20K miles and it's not getting worse. If it comes to replacing the VB, I may just deal with it for a little longer.

Sonic

Do the test, but be forewarned that the connector that DBM is talking about is VERY hard to get off.

njmaxseltd

iTrader: (19)

What exactly is it that the trans. is doing? Or not doing?

bamabob

First to second is way late - something about the 4000 rpm mark. And that's just casual acceleration, if I put a little into it, it will red line easily. Even at highway speed, say 75 at 2800 rpm, if I try to accel to even 76 the rpm shoots immediately to 4000 rpm before I feel the acceleration. I think it's just confused as it upshifts/downshifts fine, just doesn't do it when it's supposed to. The other gears shift better but I do feel what I can only characterize as backpressure - just feels like the car is being held back.

Daniel B. Martin

The Maxima factory service manual has an Automatic Transmission Symptom Chart. One of the symptoms in this table is Delayed Upshifts in Drive. The recommended Check Items are (in order) ...
1) Throttle Position Sensor (adjustment)
2) Revolution Sensor and Vehicle Speed Sensor
3) Shift solenoid valve A
4) Shift solenoid valve B