Torque Reduction - Transmission Digest

Torque Reduction

Engine torque reduction is a computer strategy that has been used in vehicles for many years now. When the selector lever is used to place the transmission into reverse or drive from either park or neutral, a command is given to reduce engine torque. This assists in providing a smooth engagement into gear. Likewise, torque reduction is commanded to take place during each upshift for smooth shifting. This strategy can also be used in vehicles equipped with adaptive cruise control or when traction control becomes activated.

Technically Speaking

  • Author: Wayne Colonna
  • Subject Matter: Smooth engagement
  • Issue: E85 flex fuel is culprit

Technical Training

Engine torque reduction is a computer strategy that has been used in vehicles for many years now. When the selector lever is used to place the transmission into reverse or drive from either park or neutral, a command is given to reduce engine torque. This assists in providing a smooth engagement into gear. Likewise, torque reduction is commanded to take place during each upshift for smooth shifting. This strategy can also be used in vehicles equipped with adaptive cruise control or when traction control becomes activated.

The strategic use of engine torque reduction varies depending on the vehicle involved. This also affects how certain codes are set reporting problems with its operation. For example, with some vehicles, if the transmission is having converter clutch issues, the traction control module (antilock braking system or ABS) may set a torque-signal code. It will do this because it’s being prohibited from requesting an engine torque reduction due to the malfunctioning transmission. Although the code is set in the ABS/traction control module, it doesn’t mean the problem is in the ABS.

When faced with engine torque reduction-error codes, a good initial diagnostic approach would be to conduct a complete health check of the vehicle. The types of codes set in other modules may reveal where the source of the problem is. If no other codes are set other than an engine torque reduction-error code, concentrate your initial focus on the engine. Look for misfire issues, bad wires, spark plugs, dirty air filter, dirty throttle body, vacuum leaks, cracks or tears in the air-intake duct work, dirty or faulty MAF sensor or TPS problems. Engine-related issues such as these can produce an engine torque-reduction error code with no other codes present making you work a little harder to find the problem. Mode 6 may also be of some help as well under these conditions.

Another item that can be added to the list that can cause an engine torque-reduction error code to set is fuel. A 2007 Pontiac Solstice with a 2.4L engine powering a 5L40E transmission came into Hardcore Automotive Inc. in Stuart, Fla., with a harsh shift complaint from another shop. The only code stored in the system was a P2637 for an invalid engine torque signal being sent to the TCM from the ECM. Harsh shifts are typically a byproduct of an engine torque-reduction error code being set.

The engine seemed to be running fine and the ECM and TCM had been replaced with no change. After clearing the code, within one mile of driving it would return. The diagnostic steps GM provides for this P2637 code is to first perform a diagnostic system check. This is the complete health check of the entire system. If any codes are set, record any freeze-frame data and record all codes. Then clear the codes drive it and see what codes set. If there are any ECM-related codes set among others, they need to be addressed first.

With only P2637 setting and no other code, along with a new ECM and TCM, it was time to focus on engine management. During this process, it was learned from the other shop that the vehicle had several codes in it before coming to Hardcore Automotive. One of them was a P0171. This is a fuel system lean code that indicates a performance problem in the fuel system.

Although this code was no longer setting, it was decided to take a look at the fuel system. Tom Johnson from Hardcore Automotive Inc. decided to check fuel pressure. In doing so he noticed that the fuel had an unusual odor and feel to it. He decided to hook into the fuel rail with an auxiliary bottle of fuel and give it a test drive. He had an immediate fix to the problem. Code P2637 did not return and the transmission shifted normally. The fuel that was in this vehicle causing the adverse condition was E85 flex fuel, a high-level ethanol-gasoline blend which contains 51%-83% ethanol. This fuel was drained and the tank was filled with regular gasoline and the problem was solved.

One last interesting piece of information, in reviewing their scan data prior to the fix, they noticed that long-term trim was running at -20. This is a big number that shows that it’s compensating for something. Apparently it had something to do with the combustion of the fuel that in turn affected engine torque management resulting in a hard-shifting transmission.

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

Sometimes, a diagnostic code is all you need

With ATSG having the opportunity to help shops solve problems, sometimes we get faced with some real doozies. A shop will call and give us a laundry list of DTCs, leaving us to think someone must have a bulkhead connector unplugged. We then go through the arduous task of deciding which codes prompted other codes

10L80 and 10R80 pump gear differences

You may have seen an article in the August 2023 issue of Transmission Digest called “GM 10L80: A new kind of pump noise,” which goes over how the front cover housing in the 10L80 is fitted with a converter drive gear and idler gear. The idler gear drives the pump’s driven gear, and is press

Spotting different 68RFE designs through the years to avoid issues

The Chrysler 68RFE has had several changes through the years. Its four-speed predecessor began with a noisy solenoid pack identified by a black colored pass-through case connector (seen in Figure 1).  Related Articles – Going the extra mile: Proving your transmission repair suspicions – Diagnosing Ford 10R60, 10R80 and 10R140 series speed sensor issues – Jatco JF613E

Sometimes, you should sweat the small stuff

It’s a common phrase: There may have been a time when you worried about something, and someone who knew what you are going through said, “Hey, don’t sweat the small stuff.” Sometimes, this may be good advice. But other times, it may be wise to handle the small stuff before it becomes bigger “stuff.”  Related