Replace the input speed sensor on the 68RFE transmission, which monitors input shaft speed for transmission control and diagnostics.

Warnings

Tools required

Parts

• Input speed sensor × 1 — Mopar 4799966AB or equivalent
• Sensor O-ring seal × 1 — Usually included with sensor

Fluids

• Mopar ATF+4 — 1.5 qt

Preparation

1. Park vehicle on level ground and apply parking brake firmly
2. Place wheel chocks behind rear wheels
3. Allow transmission to cool to ambient temperature if recently driven (minimum 30 minutes)
4. Raise front of vehicle and support securely on jack stands at frame rails
5. Verify vehicle stability before working underneath

Procedure

1. 1

   Access transmission sensor area
   From underneath the vehicle, locate the input speed sensor on the driver side of the transmission case, near the bellhousing. The sensor is positioned above the transmission pan and has a two-wire electrical connector. Clean the area around the sensor with brake cleaner to prevent contamination during removal.
2. 2

   Disconnect electrical connector
   Press the red tab on the electrical connector and pull straight away from the sensor body. Do not pull on the wires. Inspect connector terminals for corrosion or damage. If connector is stuck, use a small pry tool to gently release the locking tab.
3. 3

   Position drain pan
   Place drain pan directly below the input speed sensor location. Expect approximately 0.5 to 1 quart of ATF+4 to drain when the sensor is removed. Position the pan to catch fluid that may run along the transmission case.
4. 4

   Remove sensor mounting bolt
   Using a 10mm socket and ratchet, remove the single bolt securing the input speed sensor to the transmission case. Once bolt is loose, transmission fluid will begin to seep around the sensor. Keep bolt for comparison with new sensor hardware if replacement bolt is included.
   Torque spec

   Sensor Bolts15 Nm (11 lb-ft)
5. 5

   Extract sensor from case
   Carefully pull the sensor straight out of the transmission case bore. Fluid will drain from the opening. Allow fluid to drain completely into the pan. Remove and inspect the O-ring seal on the sensor body - it should remain with the old sensor. If O-ring stays in the transmission case bore, carefully extract it with a pick or needle-nose pliers.
6. 6

   Clean sensor bore
   Using a clean shop rag, wipe the sensor bore opening in the transmission case to remove any debris or old O-ring material. Do not allow dirt or debris to enter the transmission case. Inspect the bore for damage or scoring that could prevent proper seal.
7. 7

   Prepare new sensor
   Remove new input speed sensor from packaging. Verify it matches the old sensor design and connector type. Install the new O-ring seal onto the sensor body if not pre-installed. Lightly lubricate the O-ring with clean ATF+4 to ease installation and prevent seal damage.
8. 8

   Install new sensor
   Insert the new sensor straight into the transmission case bore, ensuring the O-ring does not roll or twist during installation. Push the sensor fully into the case until it seats against the mounting surface. Align the bolt hole in the sensor flange with the threaded hole in the case.
   Torque spec

   Sensor Bolts15 Nm (11 lb-ft)
9. 9

   Torque sensor mounting bolt
   Thread the sensor mounting bolt by hand to ensure proper thread engagement. Using a torque wrench, tighten the sensor bolt to specification. Do not overtighten as this can crack the sensor body or strip the aluminum transmission case threads.
   Torque spec

   Sensor Bolts15 Nm (11 lb-ft)
10. 10

    Reconnect electrical connector
    Push the electrical connector firmly onto the new sensor until the red locking tab clicks into place. Verify the connection is secure by gently pulling on the connector body (not the wires). Route the wiring harness away from heat sources and moving components.
11. 11

    Check transmission fluid level
    Locate the transmission fluid dipstick on the passenger side of the engine bay (red handle). With engine off and transmission cold, check fluid level. Add ATF+4 as needed to bring level to the cold range on the dipstick. Typically 0.5 to 1 quart will be needed to replace fluid lost during sensor replacement.
12. 12

    Lower vehicle and perform initial verification
    Remove jack stands and carefully lower the vehicle to the ground. Start the engine and allow it to idle. Check underneath the vehicle for any transmission fluid leaks at the sensor location. Fluid seepage indicates improper installation or damaged O-ring.

Reassembly

1. No disassembly of other components required for this procedure
2. Ensure electrical connector is fully locked onto sensor before road test
3. Verify no tools or rags were left in the work area underneath vehicle

Verification

• Start engine and shift through all transmission gear ranges (P-R-N-D-2-1) while stationary with foot on brake
• Check for diagnostic trouble codes using a scan tool - no speed sensor codes should be present
• Road test vehicle and verify transmission shifts smoothly through all gears without harsh engagements or delayed shifts
• Re-check transmission fluid level after vehicle reaches operating temperature (160-200°F) with engine idling in Park on level ground - adjust to hot range on dipstick if needed
• Perform final inspection underneath vehicle for fluid leaks at sensor after road test
• Verify speedometer and odometer are functioning correctly on instrument cluster

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