A/T - Engine Speed Sensing Problems
TECHNICAL BULLETIN # 236DATE: 1994
TRANSMISSION: 41TE/A604
SUBJECT: Engine speed Sensing Problems
APPLICATION: Chrysler
41TE/A604 Engine Speed Sensing Problems
New Transaxle Controllers
A new generation of 41TE transaxle controllers have been released with applications that retrofit back to 1989.
You will notice that between 1989 and 1992 there are two different engine groups listed one for the 3.0 liter engine and one for the 3.3 and 3.8 liter engine. Although the operating strategy of the new generation of controllers is basically the same for these two engine groups, there is one big difference between the transaxle controllers. The difference is in the way that the transaxle controller reads engine rpm.
All versions of 41TE controllers get two types of engine rpm signal. The controller gets a direct rpm signal from the engine, and a secondary rpm signal from the CCD data bus. This way the controller can tell the difference between a stalled engine and an engine rpm sensor failure. If the direct signal fails, but the CCD bus signal does not the controller knows that the direct signal is faulty, and sets a trouble code 18. If both signals show zero, it means that either the engine died, or the direct signal and the CCD bus have failed.
The big difference between the 3.0 transaxle controller and the 3.3/3.8 controller is the type of direct engine rpm signal the controller receives. The 3.0 engine transaxle controller gets a "low rate" reference signal directly from the distributor (figure 1). The 3.3 and 3.8 engines do not use a distributor. Engine speed is read from a crankshaft position sensor (figure 2).
The two types of signals are quite different and the transaxle controllers are programmed to understand one or the other but not both. If a crank sensor' type controller is installed in a 'distributor signal' car (or vise-versa), the engine rpm data can not be recognized by the controller. The unit will immediately go into the "limp-in" mode.
Your scanner will show obviously wrong engine speed readings when you check for trouble codes and data. For example: It may show 400 rpm when the engine is running much faster (3000 rpm or so). It may also show 9600 rpm at a much lower speed. even at idle. This will usually NOT set a trouble code 18. which is the code for an engine speed signal problem. Direct engine speed signals need to be almost zero for this code to set.
If you need to order a new controller compare the service part numbers listed with the vehicle year and engine size you are working on to be sure you have a matched set.
If a newly installed computer gives you incorrect engine rpm readings or goes to immediate 'limp-in' made, compare the part number of the controller you just installed, to the service part number listed to see if you have a mismatch. There are two ways to get your controller part number.
1. The paper tag on the bottom of the controller. If the paper tag has fallen off, use procedure 2.
2. Many scanners will "readout" the controller number.
Note
Disregard the "A" at the end of the number shown on your scanner.