[Buster28]

I don't know if a specific throttle position percentage causes the TCC to unlock but any upshift or downshift of the transmission will.

 

[pizzaman5000]

I don't know if a specific throttle position percentage causes the TCC to unlock but any upshift or downshift of the transmission will.

Hi Buster28,

I believe I've ruled out the TCC solenoid, I think the problem is the 4th gear slipping, or not being commanded at all. The symptom is intermittent.

When I get the P1870 code, I am above 65 mph, rpm ~3k, and it doesn't seem to shift into 4th. This is about 80% of the time.

Sometimes it does shift into 4th, which I can tell because I'm at 65+ mph and 2,400 rpm. Seems like the P1870 doesn't get thrown immediately, I'll speed up to 65+ and maintain for 5 minutes at 3k rpm and then the code pops up.

Do you know of further tests I can run to narrow down the diagnosis? I am getting my 12v LEDs today and will try to get a better idea of what the PCM is commanding. I would like to test 4th gear command, and TCC on command. Can you help determine which pins to back probe with the positive on the LED? Which pins to back probe with the negative on the LED? I still can't find a pinout diagram of the 3 connectors to the PCM.

Thank you for all your help.

 

[Buster28]

The two Shift Solenoids & Brake Band Solenoid share a common +12 Vdc reference from C3 E-14

The Control signal for two Shift Solenoids & Brake Band Solenoid is a chassis ground level signal.

The TCC solenoid control signal is +12 Vdc. The TCC solenoid control return is chassis ground.

 

[pizzaman5000]

The two Shift Solenoids & Brake Band Solenoid share a common +12 Vdc reference from C3 E-14

The Control signal for two Shift Solenoids & Brake Band Solenoid is a chassis ground level signal.

The TCC solenoid control signal is +12 Vdc. The TCC solenoid control return is chassis ground.


View attachment 128152 View attachment 128153

Thank you for your response.

I have my LEDs, I just want to confirm my understanding and make sure I won't fry anything.

I backprobe the positive of the LED to the wire side(back) of the plug as it's plugged into the PCM, and I connect the negative side of the LED to a common (chassis) ground.

Then go for a drive and observe the lighting sequence corresponding with the shifts. If 4th gear is commanded, but my rpm is 3k at 70mph, then 4th gear is slipping, 3rd gear is slipping, or my pressure is low.

If the TCC is commanded, but rpm is high and tach is responsive(moves fast with throttle changes) then the TCC is not applying.

I wont harm anything by having the LED's in parallel with the control signals?

Is the chart that I made below correct?

Thanks!

 

[Buster28]

Connect the shift solenoid Led or brake band solenoid Led in parallel with the solenoid, making sure the Led polarity is correct. The plus side of the shift solenoid Led's and brake band Led are all connected to the same point. When the Led illuminates the solenoid is energized as well. With different colored Led's you can better monitor the state of each solenoid.

For the TCC solenoid, ground the negative side of the Led.
Use small low current Led's

 

[pizzaman5000]

Connect the shift solenoid Led or brake band solenoid Led in parallel with the solenoid, making sure the Led polarity is correct. The plus side of the shift solenoid Led's and brake band Led are all connected to the same point. When the Led illuminates the solenoid is energized as well. With different colored Led's you can better monitor the state of each solenoid.

For the TCC solenoid, ground the negative side of the Led.
Use small low current Led's

Got it, so the negative for the LEDs across the shift solenoids goes to E14, and the negative for the TCC LED goes to ground.

I have these LEDs:

Amazon.com: EDGELEC 120pcs 12V LED Lights Emitting Diodes, Pre Wired 7.9 Inch DC 12 Volt 5mm LED (6 Colors x 20pcs) Assorted Kit Diffused Colored Lens- White Red Yellow Green Blue Orange Small LED Lamps : Industrial & Scientific

Amazon.com: EDGELEC 120pcs 12V LED Lights Emitting Diodes, Pre Wired 7.9 Inch DC 12 Volt 5mm LED (6 Colors x 20pcs) Assorted Kit Diffused Colored Lens- White Red Yellow Green Blue Orange Small LED Lamps : Industrial & Scientific

www.amazon.com

If this all looks good I'll go start hooking things up.

Thanks!

 

[pizzaman5000]

Got it, so the negative for the LEDs across the shift solenoids goes to E14, and the negative for the TCC LED goes to ground.

I have these LEDs:

Amazon.com: EDGELEC 120pcs 12V LED Lights Emitting Diodes, Pre Wired 7.9 Inch DC 12 Volt 5mm LED (6 Colors x 20pcs) Assorted Kit Diffused Colored Lens- White Red Yellow Green Blue Orange Small LED Lamps : Industrial & Scientific

Amazon.com: EDGELEC 120pcs 12V LED Lights Emitting Diodes, Pre Wired 7.9 Inch DC 12 Volt 5mm LED (6 Colors x 20pcs) Assorted Kit Diffused Colored Lens- White Red Yellow Green Blue Orange Small LED Lamps : Industrial & Scientific

www.amazon.com

If this all looks good I'll go start hooking things up.

Thanks!

View attachment 128156

Oh whoops, got the polarity wrong for the shift solenoids. The POSITIVE on the LEDs goes to E14, the NEGATIVE goes to A16, C2, and F14.

 

[pizzaman5000]

Connect the shift solenoid Led or brake band solenoid Led in parallel with the solenoid, making sure the Led polarity is correct. The plus side of the shift solenoid Led's and brake band Led are all connected to the same point. When the Led illuminates the solenoid is energized as well. With different colored Led's you can better monitor the state of each solenoid.

For the TCC solenoid, ground the negative side of the Led.
Use small low current Led's

See below for my understanding of this test.

 

[pizzaman5000]

See below for my understanding of this test.

View attachment 128157

Ok, well, I drove it for about an hour, everything seemed to work fine. No P1870 code, TCC solenoid lights up, 1st, 2nd, 3rd and 4th light up correctly. I don’t like that it does 3k rpm at 70mph, but maybe there’s no problem. I have 28.5” tires, I think I have the 4.3:1 rear end, and it’s not quite adding up on the rpm calculators but I didn’t get the P1870. I’m skeptical, we’ll see if it can make it the full drive cycle without that code.

 

[Buster28]

Vehicle speed at 3000 rpm is is about 10mph lower than expected for 4th gear with 28.5 diameter tires and 4.3 rear diff.

 

[pizzaman5000]

Vehicle speed at 3000 rpm is is about 10mph lower than expected for 4th gear with 28.5 diameter tires and 4.3 rear diff.

Yeah. 4th gear isn’t getting the 0.73, more like a 0.9 or something. TCC slipping, 3rd gear clutch slipping, or 4th gear clutch slipping? What further diagnostic steps would you take? I’m going to hook up the pressure test kit this weekend, and probably drop the pans and cycle the solenoids a bunch to make sure there’s no binding or “weak clicking”. I’ll refill with castrol dex/merc because I read some criticisms of the Valvoline stuff.

 

[Buster28]

If you keep the shift selector in the 3rd gear position what is the vehicle speed at 2000 rpm?

 

[pizzaman5000]

35 mph @ 2k rpm, shift selector in 3, 3rd gear indicated by LEDs and feeling the shifts, level ground, feels like steady state.

 

[Buster28]

Was the TCC solenoid energized when you observed the speedo?

 

[pizzaman5000]

Was the TCC solenoid energized when you observed the speedo?

No

 

[Buster28]

35 mph in 3rd at 2000 rpm with the TCC disengaged seems about right.

 

[pizzaman5000]

Yeah I ran it over 75 mph for 20 miles several times the last two days and it’s not throwing the p1870. I’m not sure if backprobing the solenoid control circuits did something or if it’s just intermittent failure. Previously I got the code when I went 65 for a few minutes. I cleared it 10+ times and replicated the problem trying to figure out what it was, now it’s just not doing it.