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4T60E TCC Torque Converter Clutch slipping

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The customer came in with the complaint of poor fuel economy and noticed a difference in the tachometer reading during a steady cruise. This problem was very intermittent and happened when the engine was warmed up after a long drive. After climbing a slight grade, the transmission would down shift to 3rd gear and disengage the TCC (Torque Converter Clutch). After the grade was passed the TCM (Transmission Control Module) would try to reengage the TCC. The check engine light would flash and set DTC PO740 (TCC Slip), the TCM disengaged overdrive and TCC engagement for the rest of the ignition cycle. The customer would notice at a 60 mph cruise the tachometer was almost 3000 rpm. When the transmission is working properly, the tachometer should read approximately 2500 rpm at 60 mph. We hooked up our diagnostic software for a test drive and tried to capture the data line. Using the software gave us a good look at what was happening. Figure #1 is a recording of the drive from 0 mph to a steady cruise and then back to a stop.

40fig1

This transmission uses two solenoids to control the TCC application, the TCC On/Off solenoid and the TCC PWM (TCC Duty Cycle) solenoid. These solenoids are applied simultaneously. The TCC PWM solenoid goes to 100% (Duty Cycle) when the TCM first commands it on and drops to 0% (Duty Cycle) when fully engaged. The TCC PWM solenoid is used to cushion the engagement. When the TCC PWM solenoid is at 100% it is exhausting TCC apply fluid. When the TCC PWM solenoid is at 0% the TCC is applied full pressure. You can see on Figure #1 that every time the TCM shuts off the TCC On/Off solenoid the TCC PWM solenoid will be stroked to keep the valve body bores clean of debris.

Normally when the TCC is engaged the TCC slip should be low (0-20 rpm). You can see that this recording shows the slip in more detail (Figure # 2A).

40fig2a

Notice that Figure #2B has numbers attached to it for explanation. At frame 610 you will see a marker going up and down the screen. This mark represents the point on the recording at which the data is being displayed. Lets take a look at the numbers on Figure #2B and identify them.

1. TCC on/off solenoid engages

2. TCC PWM (TCC Slip) solenoid turns on. (100% = exhaust 0% = close)

3. TCC Slip is about 165 rpm. (Slipping)

4. TCC Slip is about 83 rpm. (Slipping)

40fig2b

Here's what we found at frame 640, the TCC remains engaged but the slip speed goes up. The throttle has been opened and engine load has increased at that time. We have used my scan tool in bi-directional mode to actuate the solenoids. They have a distinctive click when they are actuated, so I believe that electrically the circuits are ok.

It sounds as though you have a TCC PWM bore that's worn out. We frequently get this call on the HelpLine. The graphs you have displayed show the TCC on/off and the TCC PWM doing their job as far as the TCM is concerned.The interestingpart is how you determined the valve body bore might be worn. Knowing the solenoids are being commanded is half the adventure. Verifying the solenoid is working is the key. The bore being worn is virtually impossible to confirm outside the vehicle

We installed a new sleeve and converter regulator valve to the valve body bore. We captured another graphic after the repair to verify the fix. Figure #3 shows normal apply and application of the TCC PWM and the TCC on/off solenoids. The slip of the TCC RPM in conjunction to the TCC PWM is now on time and working correctly.

40fig3