P0720-OUTPUT SPEED SENSOR CIRCUIT





For a complete wiring diagram Refer to Section 8W.

Theory of Operation


The transmission system uses two speed sensors, one to measure input RPM and one to measure output RPM. These inputs are essential for proper transmission operation. Therefore, the integrity of this data is verified through system checks.


  • When Monitored:

    The transmission gear ratio is monitored continuously while the transmission is in gear.

  • Set Condition:

    If there is an excessive change in the Output RPM in any gear.


Possible Causes
  
(T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT OPEN
  
(T13) SPEED SENSOR GROUND CIRCUIT OPEN
  
(T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT SHORT TO GROUND
  
(T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT SHORT TO VOLTAGE
  
(T13) SPEED SENSOR GROUND CIRCUIT SHORT TO VOLTAGE
  
OUTPUT SPEED SENSOR
  
POWERTRAIN CONTROL MODULE
  

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 42RLE - STANDARD PROCEDURE)



Diagnostic Test

1.CHECK IF THE DTC IS CURRENT



WARNING: Properly support the vehicle.



WARNING: Be sure to keep hands and feet clear of rotating wheels.



NOTE: The drive wheels must be turning at this point.




Is the Output RPM below 100?

Yes
  • Go To 2


No
  • Go To 8

2.CHECK THE PCM AND WIRING USING THE TRANSMISSION SIMULATOR



CAUTION: Removal of the Starter Relay will prevent the vehicle from being started in gear.


WARNING: The Starter Relay must be removed from the PDC. Failure to do so can result in personal injury or death.


NOTE: Failure to remove the Starter Relay can cause a Transmission - No Response condition.







Does the Input RPM read 3000 and the Output RPM read 1250 (within 50 RPM)?

Yes


No
  • Go To 3

3.CHECK THE (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT FOR AN OPEN






NOTE: Check connectors - Clean/repair as necessary.


CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller tool #8815 to perform diagnosis.




Is the resistance above 5.0 ohms?

Yes


No
  • Go To 4

4.CHECK THE (T13) SPEED SENSOR GROUND CIRCUIT FOR AN OPEN





Is the resistance above 5.0 ohms?

Yes


No
  • Go To 5

5.CHECK THE (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT FOR A SHORT TO GROUND





Is the resistance below 5.0 ohms?

Yes


No
  • Go To 6

6.CHECK THE (T14) OUTPUT SPEED SENSOR SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE








Is the voltage above 0.5 volt?

Yes


No
  • Go To 7

7.CHECK THE (T13) SPEED SENSOR GROUND CIRCUIT FOR A SHORT TO VOLTAGE



NOTE: The jumper wire must still be connected.




Is the voltage above 0.5 volts?

Yes


No
  • Using the schematics as a guide, check the Powertrain Control Module (PCM) terminals for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. Check for Service Information Tune-ups or Service Bulletins for any possible causes that may apply. If no problems are found, replace and program the PCM per the Service Information. With the scan tool, perform QUICK LEARN.
  • Perform 42RLE TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - 42RLE - STANDARD PROCEDURE)

8.INTERMITTENT WIRING AND CONNECTORS







Were there any problems found?

Yes


No
  • Test Complete.