When swapping transmissions in Mopar vehicles, particularly when aiming for OBD2 compliance and PCM control, understanding the Vehicle Speed Sensor (VSS) compatibility is crucial. This often involves navigating the nuances between the 46RH and 46RE transmissions.
The 46RH, being hydraulically controlled, isn’t directly compatible with your vehicle’s Powertrain Control Module (PCM) for electronic control. While a conversion kit exists to manage it, direct PCM integration for functions like shifting and torque converter lockup isn’t feasible.
For PCM compatibility, the 46RE, an electronically controlled transmission, is necessary. Crucially, there are variations within the 46RE models that affect VSS and speedometer integration, which are vital for OBD2 systems to function correctly.
Early 46RE transmissions featured a speed sensor at the 8 o’clock position on the tail housing, alongside a mechanical speedometer drive. This dual setup is advantageous as it accommodates both PCM speed input and traditional speedometer operation. This “early” 46RE version typically works well with adapters if you need to integrate with older speedometer systems while maintaining OBD2 VSS functionality.
Later 46RE models, however, shifted the speedometer sender to the differential. These versions retain the speed sensor on the tail housing for PCM/OBD2, but lack the mechanical speedometer drive. Integrating a speedometer with these “late” models often requires conversion, such as swapping the tail housing to an earlier 46RE type. This modification allows for both VSS signal to the PCM for OBD2 and a mechanical speedometer connection.
A third, less common tail housing type exists, primarily for early 2WD diesel applications. It has the speedo hole and a casting for the speed sensor, but the casting isn’t always drilled or tapped for sensor installation.
In summary, when dealing with 46RH/46RE swaps and OBD2 systems, identifying the specific 46RE version (early or late) is vital for VSS and speedometer compatibility. Choosing an early 46RE tail housing can simplify integration of both electronic VSS for OBD2 and mechanical speedometers. Understanding these nuances ensures a smoother transmission swap and proper OBD2 system functionality.
