Deceived - Transmission Digest

Deceived

One step many technicians take in diagnosing transmissions that have electronically controlled line-rise problems is to unplug the pressure-control solenoid. If the solenoid, pressure-regulator valve and pump are in good working order, line pressure will rise to about 150 to 170 psi at 1,000 rpm in Park. If it rose to only 80-90 psi or didn't rise at all, this would indicate that a problem existed inside the transmission.

Deceived

Shift Pointers

Author: Wayne Colonna, Technical Editor

Common diagnostic technique can produce misleading results with VW 01M

Shift Pointers

  • Author: Wayne Colonna, Technical Editor

Common diagnostic technique can produce misleading results with VW 01M

One step many technicians take in diagnosing transmissions that have electronically controlled line-rise problems is to unplug the pressure-control solenoid. If the solenoid, pressure-regulator valve and pump are in good working order, line pressure will rise to about 150 to 170 psi at 1,000 rpm in Park. If it rose to only 80-90 psi or didn’t rise at all, this would indicate that a problem existed inside the transmission.

This is a relatively reliable, “general rule-of-thumb” quick diagnostic technique, but you could be deceived if you performed this test with a Volkswagen 01M transmission. Here’s why: If you look at the hydraulics at the pressure regulator valve in Figure 1, you will notice two reducing-pressure circuits. When these circuits are charged, they prevent full line pressure from developing. And as you can see in Figure 2, these circuits are charged in the Park position. When the pressure control solenoid is unplugged in Park, line pressure will rise by only about 30% from the static or idle pressure when it was plugged in. This means about 80-90 psi. And you would be deceived into thinking that you have internal transmission problems when you do not.

To use the diagnostic technique of unplugging the pressure-control solenoid with the 01M transmission, you must place the selector lever into the Neutral or Drive range (with brake applied) to perform a full line-rise test. As you can see in figures 3 and 4, the reducing-pressure circuit with the largest area is exhausted, allowing the pressure-control solenoid to provide full boost.

These partial hydraulic schematics were taken from ATSG’s Audi/Volkswagen 01M Technician Diagnostic Guide, which provides full hydraulic schematics for both early- and late-design valve bodies. Both valve bodies function in the same manner when it comes to having two charged reducing-pressure circuits at the PR valve in Park.

You May Also Like

Sherlock Holmes Approach to an AB60 No-Move Situation

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult.  Using scopes provides

ab60

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult. 

GM 6T40 Pump Identification Guide

The 6T40 was introduced in 2008 for General Motors front-wheel-drive cars in the Chevrolet Malibu and has gone through several changes throughout its three generations, specifically in the pump area. The 6T40 is closely related to the more lightweight 6T30 and the heavier duty 6T45 and 6T50. Generation one started phasing out during the 2012

Seeing the Forest AND the Trees

They say that the proverbial phrase “I couldn’t see the forest for the trees” means that a person or organization cannot see the big picture because it focuses too much on the details. Related Articles – 4L60E Harsh 1-2 Shift – TASC Force Tips: Diagnosing 8L45 & 8L90 Shift Complaints – TASC Force Tips: Hydraulics

The Manifold Pipeway

The Honda six-speed transmission has been on the bench of many specialty shops for one reason or another (figure 1). But, for those of you who have yet to lay your hands on one, mounted on the upper side of the unit is one of the largest, if not the largest solenoid and pressure switch

8L90 Vacuum Testing

Below are the diagrams for vacuum testing GM 8L90 transmissions. Note: OE valves are shown in rest position and should be tested in rest position unless otherwise indicated. Test locations are pointed to with an arrow. Springs are not shown for visual clarity. A low vacuum reading indicates wear. For specific vacuum test information, refer

Other Posts

Shift Pointers: What to do when the 62TE TRS tab breaks

How frustrating it is when on a hot summer day, as you go to open a nice cold can of your drink of choice, and the tab breaks off? You are outside, away from any tools to remedy the problem quickly. It now requires a MacGyver mentality looking around at the resources available to get

Shift Pointers: Failures caused by incorrect tire sizes

For years ATSG has produced a wide range of issues related to improper tire sizes on vehicles. Even under-inflated tires have been known to cause issues. Problems such as premature failure with an active 4WD transfer case will occur with incorrect tire sizes. Related Articles – 10L80 and 10R80 pump gear differences – Top 20

Shift-Pointers-Jan-Figure-1-1400
Snap-on announces upgrades in diagnostic software release

With its latest diagnostic software release, Snap-on said it has added more location images and larger connector diagrams to its Fast-Track Guided Component Test feature to “give professional automotive technicians increased confidence and certainty in their diagnosis.” Related Articles – Sonnax introduces Smart-Tech clutch kit for GM 4L series – Snap-on debuts new general service

Snap-on-Announces-Upgrades-in-Latest-Diagnostic-Software-Release
Shift Pointers: Focused DTCs

On occasions when a vehicle’s computer system detects an error, it can set an array of diagnostic trouble codes. The variety and quantity of them require the ability to diagnose diagnostic codes, so it’s nice when codes set that point directly to the problem.  Related Articles – Going the extra mile: Proving your transmission repair suspicions