P1870 REVISITED
By: Jim Dial
(ATSG) Senior Technical
Consultant
Just when you thought you had all of the P1870 Torque Converter Clutch slip codes under your
belt, another vehicle comes along.... and here we go again!
I am sure that most of you are familiar with the 4L60E P1870 TCC slip code and Torque Converter
shudder problems related to the code. This was usually related to Torque Converter Regulator Valve
bore wear out, causing a loss of Torque Converter Apply pressure, allowing the Torque Converter
Clutch to slip, and we all know what fixes are available for that. Now we have a 2000 model year
Isuzu Trooper and BMW models, equipped with the 4L30-E transmission, showing up into shops
with the same P1870 code. You guessed it, the same kind of TCC Regulator Valve bore wear is the
cause here also. The biggest problem, is that there is little printed material to tell us where the TCC
regulator Valve train is located and how it works. We all know that if you don't know how it works,
you cant even begin to to fix it!
History: In the 2000 model year, Isuzu Trooper and some BMW models went to a Pulse Width
Modulated Torque Converter Clutch apply strategy. Isuzu Rodeo, Honda Passport and Cadillac Catera
stayed with the typical ON-OFF TCC apply, that they have had since day one. This strategy change,
on these limited models, has created some serious confusion in parts interchange and the
identification of parts.
Parts Change: In 2000 production, Isuzu Trooper and BMW models received the Pulse Width
Modulated Converter Clutch Apply Strategy. This created the need for a PWM Solenoid, which
happens to be the same solenoid as the 4L80-E PWM solenoid, as shown in Figure 1. This, of course,
changed the internal wiring harness because of the connector change. The pump changed from having
two valves to four valves. The additional valve trains are the Torque Converter Regulator Valve and
the Torque Converter Enable valve , as shown in Figure 2. Special Note: ATSG has named these two
valves based on valve function. If you happen to find a factory manual that names them something
else, don't be confused. The Torque Converter Control Valve also changed and now has a bore plug
with an o-ring. The pump plate and Bell housing also changed because of the valve additions, and of
course the Torque converter went to a High Carbon or woven Clutch type.
ON-OFF
PWM
Figure 1
