new PCM no overdrive

[kornfedTB]

I had to recently replace my PCM because i had a ground hog climb in my engine bay and chewed my AC wiring and it fried my old PCM so i had to order a new one from PCM of NC. Everything fixed once i put the new PCM in but now when i drove it for the first time today to work and home I noticed that it wasn't shifting into OD.

it would go through all the gears but in 4th it wouldn't go up to OD the RPMs just stayed high in the 2k when i was going 60. I never had this issue prior to then the car ran fine transmission gave me zero issues. The shift points have been higher since i put this new PCM in i have noticed.

Only check engine light code was for EVAP, its a 03 trailblazer ls with 4.2l I6, motor and trans has around 162k miles and transmission doesnt slip shifts good.

Any recommendations on things to check?

 

[mrrsm]

From @TJBaker57 ...

[SOLVED] 2002 trailblazer PCM replacement options

www.trailvoy.com

 

[kornfedTB]

The pcm was purchased from PCM of NC for a trailblazer with the same specifications as my vehicle and they programmed the VIN in it too.

It definitely goes into 4th but doesn’t TCC lock in for when I am cruising on the interstate like it use to, the rpm’s stay up in the 2k range when I’m only going 60mph. Or am I crazy and that is normal cause it doesn’t seem normal.

From @TJBaker57 ...

[SOLVED] 2002 trailblazer PCM replacement options

www.trailvoy.com

View attachment 114274

 

[TJBaker57]

If you have a scantool that can monitor live data you should monitor the TCC parameters.

If you have an inexpensive Bluetooth (or WiFi) OBD2 adapter this also can be used to monitor TCC data.

Lacking both about all you can do is verify the two related control wires that the PCM manages to control the TCC solenoid and the TCC PWM solenoid. These connect at PCM connector 2, pins 22 and 37. Both should have 12 volts present with the key in all positions except OFF.

 

[TJBaker57]

And just to clarify:

4th IS "OD", where the output shaft speed is greater than the input shaft speed.

 

[kornfedTB]

Yah I’m learning a lot from this

I hit up PCM of NC who sent me the pcm and they checked the tune and said it was a factory gm tune so the TCC lock up should work. They said to check the brake switch as it has TCC control and if that’s bad the TCC won’t lock in.

I am going to see if I can get my hands on a live data scanner and check the TCC data and see what’s going on. I have a basic one to check codes and has a little live data capabilities but I don’t think it has TCC monitoring.

 

[TJBaker57]

They said to check the brake switch as it has TCC control and if that’s bad the TCC won’t lock in.

I am going to see if I can get my hands on a live data scanner and check the TCC data and see what’s going on. I have a basic one to check codes and has a little live data capabilities but I don’t think it has TCC monitoring.

Yes, I did overlook the brake switch assembly It does indeed have a circuit devoted to the TCC lockup.

The TCC lockup brake switch can also be monitored by OBD2.

FWIW, these can all be monitored for under $20 with a Bluetooth ELM type device and a phone app. Some setup is required though. I use a Veapeak Mini Bluetooth OBD2 device from Amazon for like $15 and the Car Scanner ELM OBD2 app. That is what generated the screenshot I posted above.

What makes scantools expensive is the proprietary information the scantools makers must license from the automobile manufacturers. That's where the big money goes. It is NOT the electronics of the tool.

So if one has the information needed to converse with the vehicle and get the data one needs then the hardware device can be as cheap as these little OBD2 dongles.

EDIT: I got my threads mixed up! I haven't posted any screenshots here !!

 

[Mooseman]

A quick way to check if the TCC is locking up or not is to get up to cruising speed where it normally locks up, hold it there and tap the brake pedal with your left foot. If RPM changes up 2-300 RPM, it's working normally.

The TCC lockup solenoid may be defective. It's also possible that the bore for the TCC lockup valve in the valve body is worn and leaking. In my tune, I had the TCC PWM eliminated to reduce that bore wear and it essentially locks up instantly instead of gradually. If all else fails, try replacing the TCC solenoid. If that doesn't work, there is a TCC PWM elimination kit available to fix the bore wear in the valve body. Another possibility is the TCC itself is worn and slipping.

 

[kornfedTB]

What just baffles me is that it worked before it was parked to be repaired from the PCM getting toast and needing replaced, and now this is happening.

as mentioned by @TJBaker57 about the brake switch, when I tried the lightly press the brake pedal and see if the lock up works it didn't at all. If my brake lights still work is there still a chance that the brake switch could be affecting the TCC from not working? Cause that is my next thing to check.

@Mooseman do you by chance have any links for this TCC PWM elimination kit? I was looking around and haven't found any links to buy such kit, let alone see any photos or videos of installing it. Would that be something to do if i have to replace the TCC solenoid?

If the TCC is completely worn and slipping wouldn't it still try to get into lock up?? cause i don't think mine is even attempting to lock up at all. i will be steady going 60 at 2000-2100 rpms and holding steady with no noises or it acting like its trying to lock up.

since i replaced the PCM they said you should do a CASE relearn. I have yet to do that but i never got the code that says i need to do a CASE relearn, would that by chance cause these issues??

 

[TJBaker57]

If my brake lights still work is there still a chance that the brake switch could be affecting the TCC from not working

Tbe brake switch assembly has 3 completely separate switches inside it. So as to the TCC function it matters not a bit whether or not the brake lights work as the switch for the TCC is an entirely separate circuit within the brake switch assembly.

 

[TJBaker57]

since i replaced the PCM they said you should do a CASE relearn. I have yet to do that but i never got the code that says i need to do a CASE relearn, would that by chance cause these issues??

The service literature states the CASE learn is required upon PCM replacement regardless of a code or no code for it.

No, the CASE learn has nothing to do with the functioning of the transmission and TCC.

 

[Mooseman]

Here's the kit, which also takes care of other issues:

SK 4L60E 4L65E Transgo Shift Kit Code 1870 P1870 w/all latest updates (SK4L60E)* | eBay

Transgo Shift Kit (SK4L60E) Transgo Shift Kit (SK4L60E). Transgo Shift Kit (SK4L60E). TRANSGO SHIFT KIT. FITS: 4L60E / 4L65E / 4L70E / 4L75E. _______ A Must to remove code 1870 _______. Fixes Code 1870 Trouble.

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