Does the TCC brake switch exist on 2004 and up models?

**GP Boutique** · 11-22-2017

Like many convoluted issues with GP's, it's sometimes difficult to find specific information about the slight differences between the last generation and its predecessor. I won't bore you with my current overall issue (surging/fishbite on acceleration) but I'm currently investigation transmission/TCC related areas to see if I get any luck. I understand that the TCC solenoid commonly craps the bed in relation to this and is located on the outside of the tranny before 2004, and unfortunately requires a bit more work to get to in my 2004 GTP. Before paying a con artist to pour sawdust in my dipstick

, I found out that a TCC switch is supposedly located next to the brake light switch under the dash.

But so far I can only find diagrams and discussions on 2003 and prior GPs. Here is what it looks like (on an older Bonneville I think?) and here is the diagram for better viewing.

Now here's one of the only references to a 2004-08 brake switch I can find and I was able to find the little bugger after breaking my back and crying at the fact I had to remove a bunch of custom controls I had mounted on that bottom plastic cover

. But so far I can't find anything else related to a TCC brake switch. I'd imagine it's either been combined into one, directed to another component like the PCM, or hopefully just looks different and is somewhere else under there. But I have no clue and would really appreciate some help! I've had these surging problems for about 8 years and have essentially replaced what feels like everything but the core engine and transmission itself. A simple electronic attached to the brake would explain why the solution flew under the radar for so long....I hope.

**industrialfish** · 11-23-2017

Chasing a P0703 code?

**GP Boutique** · 11-23-2017

Originally Posted by industrialfish

Chasing a P0703 code?

Unfortunately not. I actually have come across your threads related to it when trying to find any information on the brake switch on newer models. Although I do share the same P0420 code you mentioned, but that came on at like year 6 of the problem and I no longer need to get emissions tested anyways so I ignore it. Did you ever get to changing the switch? I saw another poster saying it fixed a somewhat similar surging problem but I've never had any brake light or cruise control issues as far as I know. The only reason I'm pursuing it is because the older switches have been said to get wonky and make it seem like the TCC/Torque converter itself is at fault - not to mention potentially an easier fix. That, and when hitting the brake while going about 50mph doesn't do anything to the RPMs.

I also just got back from the dealer for a PCM update for bulletin #04-06-04-078: Hesitation, Roughness, Light Chuggle or Check Engine Light - which was a grand waste of 70 dollars

**brettstoner** · 11-24-2017

Circuit Description

The TCC release switch is part of the automatic transmission fluid pressure (TFP) manual valve position switch. The TFP manual valve position switch is mounted to the transmission valve body.
The TCC release switch is a normally-closed switch. When the TCC is released, TCC release fluid pressure opens the TCC release switch which opens the TCC release pressure circuit. When the voltage on the circuit is high, switch open, the PCM recognizes that the TCC is no longer engaged.
If the PCM detects that the TCC release switch is closed when the TCC is commanded OFF, then DTC P0742 sets. DTC P0742 is a type B DTC.
Conditions for Running the DTC

No TCC PWM solenoid valve DTC P1860.
No TCC release switch DTC P1887.
The engine torque is 95–270 N·m (70–200 lb ft).
The TP angle is 5–45 percent.
The transmission fluid temperature is 20–130°C (68–266°F).
The TCC is commanded OFF.

Conditions for Setting the DTC

The TCC release switch is closed, which indicates that the TCC is applied, 6 times for 4 seconds each during one trip.
Action Taken When the DTC Sets

The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the conditions for setting the DTC are met.
The PCM commands maximum line pressure.
The PCM commands the TCC ON at maximum capacity.
The PCM inhibits TAP Shift operation, if equipped.
The PCM freezes transmission adaptive functions.
The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
The PCM stores DTC P0742 in PCM history.

Conditions for Clearing the MIL/DTC

The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
A scan tool can clear the MIL/DTC.
The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
The PCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids

The customer may notice an engine stalling condition.
If the scan tool indicated TCC release pressure was present in Step 2 and a mechanical or hydraulic condition was not found in Step 8, an intermittent short to ground condition may exist in the TCCrelease switch signal circuit. Refer to Intermittent Conditions in Engine Controls – 3.8L.
Do not replace the torque converter for this condition, refer to Torque Converter Replacement Guide for other concerns.
Residue or contamination may cause valves to stick intermittently.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

A Yes answer indicates that the TCC Release Switch is functioning properly.

With the 20-way connector disconnected, the PCM should interpret the open circuit as TCC release pressure present.

The TCC release switch is a normally closed switch and must be disconnected to properly test for a short to ground condition. An open condition in the TCC release circuit or switch would set DTC P1887. Open circuits are not diagnosed in DTC P0742.

This step tests for a mechanical or hydraulic condition that would cause the TCC to be stuck ON.

DTC P0742

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check – Engine Controls?

—

Go to Step 2

Go to Diagnostic System Check - Engine Controls in Engine Controls – 3.8L

2

Install a scan tool.
Turn ON the ignition with the engine OFF.
NOTE

Important
Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear DTC Information function will erase the data.

Record the DTC Freeze Frame and Failure Records.
Clear the DTCs.
Start the engine.
With a scan tool, observe the TCC Release Pressure status.

Does the scan tool indicate Yes for TCC Release Pressure?

—

Go to Step 3

Go to Step 4

3

Drive the vehicle above 72 km/h (45 mph) in D3 or D4, with a TP angle of 5–45%.
With the scan tool, command the TCC PWM solenoid valve ON and observe TCC Release Pressure.
With the scan tool, command the TCC PWM solenoid valve OFF and observe TCC Release Pressure.

While the TCC was commanded OFF did the TCCrelease pressure indicate NO at any time?

—

Go to Step 8

Go to Diagnostic Aids

4

Turn OFF the ignition.
Disconnect the AT inline 20-way connector. Additional DTCs may set.
Turn ON the ignition with the engine OFF.
Observe the TCC Release Pressure status.

Does the scan tool indicate Yes for TCC release pressure?

—

Go to Step 5

Go to Step 6

5

Disconnect the transmission internal wiring harness from the TFP manual valve position switch.
Test the signal circuit of the TCC release switch for a short to ground between the AT inline 20-way connector and the TFP manual valve position switch.
Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.
Did you find the condition?

—

Go to Step 10

Go to Step 7

6

Test the signal circuit of the TCC release switch for a short to ground between the PCM and the AT inline 20-way connector.
Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?

—

Go to Step 12

Go to Step 11

7

Remove the TFP manual valve position switch.
Inspect the TCC release switch for the following conditions:
- A damaged or leaking seal
- Sediment or debris
- Damaged switch contacts
- Stuck switch contacts

Did you find a condition?

—

Go to Step 9

Go to Step 8

8

Inspect for the following conditions:
- TCC control valve stuck in the apply position
- TCC PWM solenoid valve stuck, exhaust restricted or faulty internal O-ring
- TCC fluid circuits leaking
  Refer to in Transmission Unit Repair Manual.
- The TCC blowoff valve or spring for damage or not seating
  Refer to in Transmission Unit Repair Manual.
- Turbine shaft seals for leaks
  Refer to in Transmission Unit Repair Manual.
- Pump shaft seal for leaks
  Refer to in Transmission Unit Repair Manual.
- Spacer plate gaskets torn/leaking
  Refer to in Transmission Unit Repair Manual.
- Pressure regulator valve stuck
  Refer to in Transmission Unit Repair Manual.
- Abnormally high or low line pressure. Refer to Line Pressure Check.
Repair or replace any malfunctioning components.

Did you find and correct a condition?

—

Go to Step 12

Go to Diagnostic Aids

9

Replace the TFP manual valve position switch.
Refer to Transmission Fluid Pressure Manual Valve Position Switch Replacement.
Did you complete the replacement?

—

Go to Step 12

—

10

Replace the transmission wiring harness assembly.
Refer to Wiring Harness Replacement.
Did you complete the replacement?

—

Go to Step 12

—

11

Replace the PCM.
Refer to Powertrain Control Module Replacement in Engine Controls – 3.8L
Did you complete the replacement?

—

Go to Step 12

—

12

In order to verify your repair, perform the following procedure:

Select DTC.
Select Clear DTC Information.
Operate the vehicle under the following conditions:
- Drive the vehicle in a DRIVE range.
- TP angle must be 5–45 percent.
- The engine torque is 95–270 N·m (70–200 lb ft).
- The TCC must be commanded OFF.
- The TCC release switch must be open, indicating TCC release pressure is present, for 3 seconds.
Select specific DTC.
Enter DTC P0742.

Has the test run and passed?

—

Go to Step 13

Go to Step 2

13

With a scan tool, observe the stored information, capture info and DTC info.
Does the scan tool display any DTCs that you have not diagnosed?

—

Go to Diagnostic Trouble Code (DTC) List in Engine Controls – 3.8L

System OK

**brettstoner** · 11-24-2017

So it is internal inside the transmission.

There is a brake pedal position sensor which runs to the body control module. The BCM sends the data on the CANBUS line and also outputs for the stop lamp switch signal.

**GP Boutique** · 11-25-2017

Originally Posted by brettstoner

So it is internal inside the transmission.

There is a brake pedal position sensor which runs to the body control module. The BCM sends the data on the CANBUS line and also outputs for the stop lamp switch signal.

Well damn. The 'customer' also hasn't had any stalling issues, even when I pulled one of the transmission fuses/relays and it drove like I was towing a house. At this point, I wouldn't rule out some crazy short in the wiring somewhere in this process of signaling the torque converter to lock or unlock. Whether that's the brake pedal sensor, which is more unlikely since they are no longer separated into two brake light + cruise control and TCC plungers, or the TCC solenoid itself, I have no clue. I've yet to receive any transmission related codes in the life of the car, but I also received no codes for the 4 years my ABS module was busted, so call me crazy.

Went out for another test drive tonight with the Torque app comparing the PID for the TCC slip speed and the engine speed. As far as I understand:

At a stop in gear, the slip speed should be almost exactly matching the engine speed with single digit variation at most.
With normal city stop n' go driving or getting up to overdrive speeds, the slip speed should bounce around a few hundred RPMs below the engine speed
In 4th/OD, when the torque converter is supposedly locked, the slip speed should be essentially locked at 0, although I've read in various places a variation of up to even a hundred or so RPMs above 0 is acceptable as something normal.

As for my results, it was very difficult to do this with my luck of traffic and having to pay attention to my poorly mounted cell phone with Torque running. I took two interesting shakey shots with my other phone which I'll just write out. I only took them once the numbers stayed roughly the same for at least 10 seconds while holding the throttle steady. I had a TCC slip of 17 RPM/engine 1414 RPM at 51mph and the other shot was (after doing a u-turn and going down the same flat road) was a TCC slip of -170 RPM/engine 1368 RPM at 52mph. Since I also read the TCC slip is a calculation of gear ratios compared to the engine speed, it can sometimes show up in a negative. But these seem like two wildly different numbers with only one mph difference. Otherwise, everything else matches up at a stop and slips normally when just driving around like grandma.

Unfortunately, I couldn't tell if the slip numbers did anything different when I would force the surging to happen under heavy loads/hard acceleration since I was too busy reining the car back in

Sorry for the long-winded technical posts. I'm just so desperate to find out what the hell has been plaguing this otherwise magnificently reliable vehicle for the past 8 years, even if I don't ever get to fix it. I'm starting to doubt the transmission at this point considering how long this has been going on without anything crazy breaking. Looking at other TCC solenoid problem posts, there's usually an element of hard shifting or stalling or some other issue that would make simple driving a pain. If you're just in the city and don't have to merge into traffic at a high rate of acceleration from a stop or run from the police, then you'd have no idea anything is wrong with the car.