[pizzaman5000]

Hello,

Recently got my Passport running after sitting for a year. Did a transmission fluid/filter change, some clutch material in pan, not terrible. While driving on the highway at 60mph, the dummy lights came on, and the code was P1870. I've done some research, and I think it's either(in order of hopefulness):

1. TCC solenoid gummed up or failed
2. Vehicle output speed sensor failed/failing
3. TCC friction material gone
4. Pump not producing enough pressure to lock up TCC

Can the 4L30E throw a P1870 if the TCC solenoid is bad? Wouldn't it throw a P1860 instead? Can a failing vehicle speed sensor cause a mismatch between the input and output speed readings and cause a P1870?

I am going to test the solenoid from the connector on the outside of the trans, I believe it has to have a resistance between 17.5 ohms and 18.5 ohms to pass.

Thank you in advance, I'm going to go crawl under my truck in the rain and see if I can get a resistance on the TCC solenoid.

 

[Shawn Anthony]

Is there not a freeze frame of the event?
The freeze frame should provide all the information to determine if its clutch slippage. If not I know a trick to test the system.

 

[pizzaman5000]

I don’t think my scanner got freeze frame data. I’ll see if I can access that. How can I test TCC slip?

thanks.

 

[pizzaman5000]

I don’t think my scanner got freeze frame data. I’ll see if I can access that. How can I test TCC slip?

thanks.

Is there not a freeze frame of the event?
The freeze frame should provide all the information to determine if its clutch slippage. If not I know a trick to test the system.

I found the freeze frame data:

RPM: 2884
Intake manifold pressure: 88 kPa
Mass airflow rate: 63.93 g/s
Throttle position: 34.1%
vehicle speed: 68.93 mph

I’ll try to Google some answers from this but any help is appreciated

thank you

 

[Shawn Anthony]

I found the freeze frame data:

RPM: 2884
Intake manifold pressure: 88 kPa
Mass airflow rate: 63.93 g/s
Throttle position: 34.1%
vehicle speed: 68.93 mph

I’ll try to Google some answers from this but any help is appreciated

thank you

That's a small freeze frame.
Can your scanner read live data via ABS computer? If so I know a really good way to test for clutch slippage.

 

[pizzaman5000]

That's a small freeze frame.
Can your scanner read live data via ABS computer? If so I know a really good way to test for clutch slippage.

I believe it can, I'll have to boot it up next time I'm driving.

What's the test?

Thanks

 

[Shawn Anthony]

This test will compare the input shaft speed and the output shaft speed. By using the vehicles wheel speed sensor and Vss. if the clutch slips you will see a discrepancy in the shaft speeds.

The first step is to verify normal speed or the speed ratio between the rear wheel speed sensor and the vehicle speed sensor. Drive your vehicle in first gear at 3,500 RPM. View the live data and monitor your wheel speed and vehicle speed. The values they display is your baseline. For example; With the engine at 3500 RPM in first gear your live data will display a vehicle speed of 15 miles an hour and a wheel speed of 28RPM. (These numbers are not actually readings in this example) Because the rear drive shaft does not have a clutch this is what you should see when you test the clutch on the front axle.

Step 2
Shift into 4wd & Apply the parking brake about 2/3 or enough to make the tires drag. The parking brake will hold the rear brakes which will transfer the engine power to the front axle and the extra weight and drag caused by the rear brakes will increase the clutch load.

Drive the vehicle forward in first gear at 3500RPM for a 3 to 4 seconds while viewing live data. If your scanner can record live data use that function.

Step 3 is to interpret the numbers.
- If your transfercase clutch is slipping, you will notice the vehicle speed will be greater than your baseline vehicle speed and your wheel speed will be lower than the baseline wheel speed.

- If your vehicle speed and your wheel speed match the baseline speed, your clutch is not slipping.

- If the vehicle doesn't move at all your clutch is not engaging.

A small warning...
Your transmissions torque converter won't like this test and you will feel it lock up....that's normal. What's not normal is the extra heat it will cause. I wouldn't advise performing this test for more than 4 seconds. If you must repeat this test I would let your transmission cool for minimum of 5 minutes.

 

[mudoilngears]

- If your transfercase clutch is slipping, you will notice the vehicle speed will be greater than your baseline vehicle speed and your wheel speed will be lower than the baseline wheel speed.

What is a transfercase clutch in a 97 passport?

 

[pizzaman5000]

This test will compare the input shaft speed and the output shaft speed. By using the vehicles wheel speed sensor and Vss. if the clutch slips you will see a discrepancy in the shaft speeds.

The first step is to verify normal speed or the speed ratio between the rear wheel speed sensor and the vehicle speed sensor. Drive your vehicle in first gear at 3,500 RPM. View the live data and monitor your wheel speed and vehicle speed. The values they display is your baseline. For example; With the engine at 3500 RPM in first gear your live data will display a vehicle speed of 15 miles an hour and a wheel speed of 28RPM. (These numbers are not actually readings in this example) Because the rear drive shaft does not have a clutch this is what you should see when you test the clutch on the front axle.

Step 2
Shift into 4wd & Apply the parking brake about 2/3 or enough to make the tires drag. The parking brake will hold the rear brakes which will transfer the engine power to the front axle and the extra weight and drag caused by the rear brakes will increase the clutch load.

Drive the vehicle forward in first gear at 3500RPM for a 3 to 4 seconds while viewing live data. If your scanner can record live data use that function.

Step 3 is to interpret the numbers.
- If your transfercase clutch is slipping, you will notice the vehicle speed will be greater than your baseline vehicle speed and your wheel speed will be lower than the baseline wheel speed.

- If your vehicle speed and your wheel speed match the baseline speed, your clutch is not slipping.

- If the vehicle doesn't move at all your clutch is not engaging.

A small warning...
Your transmissions torque converter won't like this test and you will feel it lock up....that's normal. What's not normal is the extra heat it will cause. I wouldn't advise performing this test for more than 4 seconds. If you must repeat this test I would let your transmission cool for minimum of 5 minutes.

Thanks. This test sounds a little harmful to the torque converter clutch, which I think may be worn already. I may try this if I can't figure out a simpler diagnosis for the TCC, but I think my first step is to resistance test the TCC solenoid, then I will try to figure out if I can test the TCM output to see if it is signaling the solenoid appropriately. If the TCM is signaling and the solenoid has a resistance of 17-24 ohms, I may try to apply 12v to the solenoid to see if it clicks. If all this works then I think the problem is either with the valve that the TCC solenoid controls, or the TCC clutch material is gone, or the pump is not supplying enough pressure to engage the TCC. I want to have a rock solid diagnosis before I am forced to drop the transmission and replace the converter or whatever.

Thanks for the reply

 

[Buster28]

The Powertrain Control Module (PCM) in your 97 Passport is comparing the engine rpm with the transmission tail shaft rpm, the tail shaft rpm is being counted by the transmission "speed sensor" mounted to the transmission extension housing. DTC P1870 is set when the PCM determines that the difference between input and output rpm with the TCC applied is more than expected during the slip test. It may be that the TCC is slipping or the 3rd clutch or 4th clutch is slipping or the TCC solenoid is not working.

Step 1. Measure the TCC solenoid resistance between the signal wire at the PCM end and the negative battery terminal. I think the TCC solenoid connection at the PCM is on connector C-2 Pin D2 and is a Red/Yellow wire. Make the resistance measurement with the connector disconnected from the PCM. The TCC signal wire goes to pin 4 of the overdrive section 5 Pin connector.

NOTE that one side of the TCC solenoid coil is connected to the case inside the transmission ("grounded"), and if the transmission case is not grounded properly to the engine block the TCC solenoid won't operate.

 

[pizzaman5000]

Thank you! I couldn't find that diagram. I have the ATSG 4L30E techtran manual, but it's not showing me the pinout of the pcm and there are a lot of red/yellow wires. I am going to measure resistance and get back to you. I am also going to go buy a high/low trans pressure test kit today. My suspicion is that this trans will need a rebuild or a new torque converter, it has 190k on it and the fluid was dark when I bought it. I did one spill and fill, but didn't drop the pan and change the filter, and then the head gasket blew and it sat for a year before I did the head gasket. I ran it for about 100 miles testing the head gasket before changing the trans fluid and filter. I bet I pushed clutch material up into the TCC valve or something. All other shifts are flawless, besides a bit of hesitation into 2nd when it's cold. Only for the first couple shifts from 1-2 though.

Thanks for the diagram.

 

[pizzaman5000]

The Powertrain Control Module (PCM) in your 97 Passport is comparing the engine rpm with the transmission tail shaft rpm, the tail shaft rpm is being counted by the transmission "speed sensor" mounted to the transmission extension housing. DTC P1870 is set when the PCM determines that the difference between input and output rpm with the TCC applied is more than expected during the slip test. It may be that the TCC is slipping or the 3rd clutch or 4th clutch is slipping or the TCC solenoid is not working.

Step 1. Measure the TCC solenoid resistance between the signal wire at the PCM end and the negative battery terminal. I think the TCC solenoid connection at the PCM is on connector C-2 Pin D2 and is a Red/Yellow wire. Make the resistance measurement with the connector disconnected from the PCM. The TCC signal wire goes to pin 4 of the overdrive section 5 Pin connector.

NOTE that one side of the TCC solenoid coil is connected to the case inside the transmission ("grounded"), and if the transmission case is not grounded properly to the engine block the TCC solenoid won't operate. View attachment 127614

Ok, I am getting 16.6 ohms, which is just outside the 17-24 ohm range? It seems like I shouldn't be able to get a lower reading unless there's a problem with the solenoid, but also it is just barely under. The solenoid is fairly easy to change and only $50.

 

[Buster28]

Pull out the 5 pin connector on the overdrive case to be sure your reading the correct pin on the PCM , it the reading goes from 16.6 to zero your on the correct pin . 16.6 is close to expected so likely not a solenoid problem.

 

[pizzaman5000]

Can I connect battery positive to that pin on the solenoid while under the truck and listen for solenoid clicks?

If solenoid is ruled out, next step is pressure testing the trans following the procedure in the ATSG manual?

thank you

 

[Buster28]

Reverse Locked Out
When the vehicle is moving forward above approximately 7 mph and Reverse (R) gear range is selected, the PCM/TCM energizes the TCC solenoid. With the TCC solenoid energized, solenoid feed fluid flows through the solenoid and fills the solenoid signal fluid circuit. Solenoid signal fluid is routed to the spring end of the reverse lockout valve, thereby assisting spring force to keep the valve closed against reverse fluid pressure. This blocks reverse fluid from entering the reverse clutch fluid circuit and prevents the transmission from shifting into Reverse.

Therefore if you applied +12 Vdc to the solenoid causing it to energize with the engine running in Park it should prevent Reverse from being selected when the shifter is moved to the R position.

 

[pizzaman5000]

Reverse Locked Out
When the vehicle is moving forward above approximately 7 mph and Reverse (R) gear range is selected, the PCM/TCM energizes the TCC solenoid. With the TCC solenoid energized, solenoid feed fluid flows through the solenoid and fills the solenoid signal fluid circuit. Solenoid signal fluid is routed to the spring end of the reverse lockout valve, thereby assisting spring force to keep the valve closed against reverse fluid pressure. This blocks reverse fluid from entering the reverse clutch fluid circuit and prevents the transmission from shifting into Reverse.

Therefore if you applied +12 Vdc to the solenoid causing it to energize with the engine running in Park it should prevent Reverse from being selected when the shifter is moved to the R position.

Whoa so if your TCC isn’t working and you accidentally shift into reverse on the Highway you shred your transmission huh? How do you know all this stuff? I will try and get a pigtail from the junkyard so that I can isolate the TCC solenoid pin and run a wire to the positive on the battery with a switch. Then I can manually operate the TCC solenoid… but can I run the vehicle with that connector disconnected? I’ll pick up the line pressure test kit today after work and try to test that so I can maybe get some more data on what is wrong.

thank you

 

[Buster28]

You could also connect a 12 LED between PCM connector C-2 D2 and ground to see if the PCM is actually sending On/Off commands to the TCC solenoid. You should be able to stick the LED wire into the wire side of the connector and make electrical contact. The positive side of the LED goes to the connector.
Btw, not all 4L30e transmissions have the Reverse Lockout feature but I am reasonably sure your 97 does.

 

[pizzaman5000]

You could also connect a 12 LED between PCM connector C-2 D2 and ground to see if the PCM is actually sending On/Off commands to the TCC solenoid. You should be able to stick the LED wire into the wire side of the connector and make electrical contact. The positive side of the LED goes to the connector.
Btw, not all 4L30e transmissions have the Reverse Lockout feature but I am reasonably sure your 97 does.

I have a few more observations, but I haven't been able to get to any more test data.

When driving on the highway, I can feel the trans go into lockup when I get above 50 mph and let off the gas. The rpm will drop from about 2200 to 1700 or so, and I can feel engine braking and lockup. As soon as the vehicle speed drops to 50 mph, lockup disengages and the rpm goes up to 2100-ish. If I depress the gas pedal while in lockup above 50 mph, it immediately disengages. Any throttle disengages lockup, even 10%.

I have not gotten a p1870 for about a week, but I think I would have to get above 50 mph, and maintain throttle at under 30% for the computer to command lockup and not get it due to throttle. I am going to test this ASAP.

I also occasionally get a "R.abs" light and the parking brake light will remain illuminated. This is intermittent, and I assumed it was due to low brake pads in the rear, or parking brake adjustment.

Is it possible that there is some issue with my brakes that is causing either excess throttle to maintain speed which is preventing TCC lockup, or could a brake problem by itself keep the TCC from lockup?

I am still planning on testing transmission pressures, and applying 12v to the solenoid pins to listen for clicking, but I think the solenoid may not have any issues. I've been researching transmission rebuilds and I think it's something I am interested in taking on and doing some hands on learning, but I have to do the best I can with diagnosis first. I'll get into my brakes and the transmission testing ASAP.

Thank you

 

[Buster28]

The TCC will unlock when the foot brake switch operates, if the switch is out of adjustment road conditions could cause it to randomly operate causing erratic TCC operation.

 

[pizzaman5000]

The TCC will unlock when the foot brake switch operates, if the switch is out of adjustment road conditions could cause it to randomly operate causing erratic TCC operation.

Do you know what throttle percent will disengage the TCC during normal operation?

Thanks