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Chris (aka- Moose)
Chris (aka- Moose), Technician
Category: Transmissions
Satisfied Customers: 47984
Experience:  16 yrs. experience with auto, manual, & CVT drivelines
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Chevrolet Suburban K1500 4x4: I have a 1999 Chevrolet k1500

Customer Question

I have a 1999 Chevrolet k1500 Suburban 4x4, 6.5 turbo diesel with the 4L80e transmission. I just had the transmission rebuilt. When it locks up in overdrive the lockup slips and gives a p1870 error code. The TCC kit and the pressure selenoid sonnax kits have been put in and both selenoids have also been replaced. The torque converter has been replaced. None of these has fixed the slipping in lockup. It slips at 60% to 73% power and goes over 156 rpm slippage.
Submitted: 2 years ago.
Category: Transmissions
Expert:  Chris (aka- Moose) replied 2 years ago.
Have you done any testing at the valve body to check the components used to lock up the converter?
Customer: replied 2 years ago.
That was the part of the problem discussion to begin with; TCC selenoid and the TCC valve kit by Sonax. This was done for the TCC as well as the pressure valve and selenoid. This was done by the professional. This is why we cannot figure out what is wrong. The torque converter has been changed 3 times. Now another rebuilt transmission was put in with the same kits and it still slips in overdrive lockup with the same parameters. It locks up just fine. It just slips when under pressure going about 63mph uphill. Then it gives the p1870 error.
Expert:  Chris (aka- Moose) replied 2 years ago.
The TCC solenoid is pulse width modulated with a ground control from the PCM. Can you remove this wire from the transmission, and run it into the cab. Then get into a lockup situation, and ground the wire to a seat bolt for instance. That way you know the ground is good with no OHMS. Then monitor to see if there is slippage still occurring. This will tell us if the PCM on wiring has an issue. You want a excellent 5 star answer & I would like to be rated the same for providing it. Consider I don't know your skill level & I can't see, smell, hear, or touch the vehicle. It may take a few back and forth replies. Try your best to respond with good detail so I can do the same. I normally log in at 3pm and work late. A rating is required. Your rating me, what I type. I am not an employee of this website, nor have control over the fees or the time it took to get a response. If you rate negative or not at all you still paid, but I get nothing. I want you pleased with me and my efforts, so let me know if your experience here has come up short.Thanks Chris
Customer: replied 2 years ago.
The TechII machine already tells us that the torque converter is locking up. The lockup is slipping. I don't know if it is slipping because the PCM/ECM is trying to hold it in lockup when there is too much pressure/torque or if the pulse width is not sufficient to hold it in place. Before the transmission rebuild the transmission did not have this problem. It took 3 seconds to engage reverse and was giving errors for 2nd gear shifting. The rebuild fixed those problems but this slipping in lockup is a problem it never had and now gives the p1870 error and slips over 156 rpm at 63mph with 73% power. It clearly gets a lockup signal.
Expert:  Chris (aka- Moose) replied 2 years ago.
Since you have done this test and ruled out the converter, and all things in the transmission, there is nothing else I can think of to check.