TO: All ATP Technicians
FROM: James Strong, Customer/Technical Service Manager
RE: Chrysler A604 (41TE) and 42LE Vehicle Speed Sensors (VSS)
The Vehicle Speed Sensor (VSS) is more than a digital version of the speedometer cable. In fact, using the VSS to generate digital speedometer readings is a relatively recent application for the VSS.
With OBD-II, the Engine Control Module (ECM) controls ignition timing as well as fuel delivery resulting in engine operating performance. This is considered and/or accomplished through vehicle speed.
Automatic transmissions use VSS to provide torque converter clutch operation, determine proper shift points, and monitor gear ratios. VSS are also used as safety devices. If the vehicle is traveling too fast, the electronic signal from the VSS is sent to the ECM to cut off fuel delivery to slow the vehicle down.
The VSS can be easily damaged when the transmission is removed for major service, high under hood or internal transmission temperatures and/or the sensor component has failed.
In the Chrysler’s A-604 (41TE) and the 42LE transmissions, the VSS signals are constantly compared from the two speed sensors to monitor gear ratios. If at any time during normal vehicle operation, the ratio that the computer calculates does not match the gear ratio, the computer will set off a gear ratio error code. If the computer notices a major change in the signal from one of the sensors while it is operating, it will set off a code for that individual sensor.
Prior to 1991, there was only one code available to indicate a problem in these sensors, trouble code 39. If this code is experienced, it is important to find out much as possible about this transmission operating condition that occurred right before the unit went into limp-in mode. These conditions will be the only clues you may have to identify the cause of the failure and the source of the code.
However, on 1991 and later models, the computer sets a specific code for the gear range or the sensors involved in which, identifying and isolating the problem is much easier. Below is a chart explaining the trouble codes, scan tool display, SAE P code, and if the transmission is in limp in/out mode.
| Trouble Code
||Scan Tool Display
||SAE P Code
||Limp In/Out Mode|
||Gear ratio error (pre-1991 only)
||Gear ratio error in reverse
||Gear ratio error in 1st gear
||Gear ratio error in 2nd gear
||Gear ratio error in 3rd gear
||Gear ratio error in 4th gear
||Turbine shaft sensor error
||Output shaft sensor error
||Sensor ground is loose/damage
Obvious signs that the VSS is not producing a signal include the speedometer/odometer not working, the cruise control cannot be set, and transmission shifting is rough and erratic. Other possible problems from a failed VSS include rough idling and an increase in fuel consumption.
ATP-Inc has introduced (2) new part numbers for the vehicle speed sensors (VSS) fitting 1989-2007 Chrysler’s A604 (41TE) transaxle and the 42LE transmissions.
Input (Turbine) Speed Sensor, part no. TE-7 and Output Speed Sensor, part number TE-8 can now be ordered to replace these failure prone speed sensors.
Visit our website at www.atp-inc.com for updated product information and Tech Direct® Bulletins.