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The Input and Output Speed Sensors are two-wire magnetic pickup devices that generate AC signals as rotation occurs. They are mounted in the left side of the transmission case and are considered primary inputs to the Transmission Control Module (TCM).
Note:
The 42RE transmissions use a single sensor (located on the overdrive gear case, over the park gear).
The 45RFE / 545RFE transmissions use two sensors, an input speed sensor and an output speed sensor. Both are the same part number.
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Operation:
The Input Speed Sensor provides information on how fast the input shaft is rotating. As the teeth of the input clutch hub pass by the sensor coil, an AC voltage is generated and sent to the TCM. The TCM interprets this information as input shaft rpm.
The Output Speed Sensor generates an AC signal in a similar fashion, though its coil is excited by rotation of the rear planetary carrier lugs. The TCM interprets this information as output shaft rpm.
The TCM compares the input and output speed signals to determine the following:
- Transmission gear ratio
- Speed ratio error detection
- CVI calculation
The TCM also compares the input speed signal and the engine speed signal to determine the following:
- Torque converter clutch slippage
- Torque converter element speed ratio
Sensor failure:
Failure of the Transmission Input Shaft Speed Sensor and/or the Output Shaft Speed Sensors are somewhat common on early model WJ Grand Cherokees. Diagnostic Trouble codes that may be tripped are:
P0500 - No vehicle speed sensor signal
P0720 - Low Output SPD Sensor RPM Above 15 MPH
The relationship between the Output Shaft Speed Sensor and vehicle speed is not within acceptable limits.
P0720 - Low Output SPD Sensor RPM Above 15 MPH
Output shaft speed is less than 60 rpm with vehicle speed above 15 mph (4-speed auto. trans. only).
P0721-P0723 - Sensor circuit range, performance, no signal
Speed sensor removal
1. Raise vehicle.
2. Place a suitable fluid catch pan under the transmission.
3. Remove the wiring connector from the input speed sensor.
4. Remove the bolt holding the input speed sensor to the transmission case.
5. Remove the input speed sensor from the transmission case.
Speed sensor installation
1. Install the input speed sensor into the transmission case.
2. Install the bolt to hold the input speed sensor into the transmission case. Tighten the bolt to 105 in.lbs. (11.9 N·m).
3. Install the wiring connector onto the input speed sensor
4. Verify the transmission fluid level. Add fluid as necessary.
5. Lower vehicle.
| WJ speed sensors |
Output speed sensor for 42RE transmission
(1999-2004) | P/N 4800879
(supercedes P/N 4412879) | List price: $18.35 |
Input speed sensor for 45RFE / 545RFE transmission
(1999-2005) | P/N 4799061AB | List price: $36.70 |
Output speed sensor for 45RFE / 545RFE transmission
(1999-2005) | P/N 4799061AB | List price: $36.70 |
(Prices listed are for reference purposes only and may vary by dealer. Parts are not available from this web site.)
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