Signal Too Low
Signal too low
Checking the transmission output speed sensor signal
- Ignition off
- Raise the car so that the drive wheels are clear of the ground
- Start the engine. Allow the engine to idle
- Shift gear selector to position D so that the drive wheels begin to rotate
- Read off the transmission speed.
Depress the accelerator pedal (AP) and check that the speed is updated.
Note! Ensure that the wheels are not rotating when the gear selector is moved.
Note! Diagnostic trouble codes (DTCs) may be stored in the ABS system when the rear wheels are stationary and the front wheels rotate. Erase any diagnostic trouble codes (DTCs) stored in the ABS system after fault-tracing.
Was the speed updated?
Yes - Intermittent fault
No - Checking the wiring
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Checking the wiring
- Ignition off.
Check the power supply cable between control module terminal #57 (#A57) and speed sensor connector terminal #1. Check for an open-circuit. Check for a short-circuit to ground.
Check the signal cable between control module terminal #39 (#A39) and speed sensor connector terminal #2. Check for an open-circuit. Check for a short-circuit to ground.
Remedy as necessary.
Other information
- To connect the breakout box, see Connecting the breakout box, 4T65EV-GT Connecting the Breakout Box
- To check or replace the transmission output speed sensor, see Output speed sensor gearbox, replacing Transmission Output Speed Sensor, Replacing
- For information about signals, see Signal specification, 4T65EV-GT Signal Specification
- Checking wiring and terminals Checking Wiring And Terminals
Was a fault detected?
Yes - Verification
No - Checking the control module
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Checking the control module
- Ignition off
- Connect the breakout box to the control module
- Disconnect the connector for the speed sensor
- Connect a temporary cable between terminals #A35 and #A57 on the breakout box
Caution! Check that the temporary cable is connected to the correct terminals. Also check that there is no risk of unintentional short-circuits.
- Ignition on
- Read off the status.
Check that the status is "1" when the temporary cable is connected to the terminals above.
Disconnect the cable end that is connected to terminal #A35 and move the cable to terminal #A53.
Note! Leave the cable end connected to terminal #A57 (#A57) in place.
Check that the status changes to "0" when the temporary cable has been moved to terminal #A53.
The transmission speed sensor is defective if the status has changed between "1" and "0" as above and no errors have been detected on the cables or terminals in the preceding checks. Replace the transmission speed sensor if this is the case.
The transmission control module (TCM) is defective if the status has not changed between "1" and "0" as above and no errors have been detected on the cables or terminals in the preceding checks. If this is the case replace the control module.
Other information
- To connect the breakout box, see Connecting the breakout box, 4T65EV-GT Connecting the Breakout Box
- To connect the breakout box to the transmission connector, see Connecting the breakout box, GM automatic transmissions, 4T65EV-GT Connecting the Breakout Box, GM Automatic Transmissions
- To check or replace the transmission output speed sensor, see Output speed sensor gearbox, replacing Transmission Output Speed Sensor, Replacing
- To replace the transmission control module (TCM), see Transmission control module (TCM), replacing, B5254T2, AW50/51 AWD, B5254T2, AW55-50/51SN Service and Repair
- For information about signals, see Signal specification, 4T65EV-GT Signal Specification.
Continue - Verification
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Verification
Verification
Hint: After carrying out the repair, check that the fault has been remedied.
- Ignition off.
- Reinstall connectors, components etc.
- Raise car so that drive wheels are unimpeded.
- Start the engine and let it idle.
- Shift gear selector to position D so that the drive wheels begin to rotate.
- Read off the transmission speed.
Check that speed is updated
Note! When the rear wheels are stationary and the front wheels rotate, diagnostic trouble codes (DTCs) can be stored in the ABS system. Erase any diagnostic trouble codes (DTCs) stored in the ABS system after fault-tracing.
Note! Ensure that the wheels are not rotating when the gear selector is moved.
Was speed updated?
Yes - Verification completed
No - Fault-tracing information
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Fault-tracing information
Information
Fault-tracing information
The fault should have been detected and remedied. As this is not the case fault-tracing has failed.
Exit fault-tracing for this diagnostic trouble code (DTC) or make another attempt.
Do you want to exit fault-tracing?
Yes - Exit Fault-Tracing
No - Attempt New Test
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Attempt New Test - Checking the transmission output speed sensor signal
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Intermittent fault
- Ignition off.
Check the control module and transmission output speed sensor connectors. Check for contact resistance and oxidation.
Check the power supply cable between control module terminal #57 (terminal #A57) and speed sensor connector terminal #1. Check for an intermittent open-circuit. Check for an intermittent short-circuit to ground.
Check the signal cable between control module terminal #39 (terminal #A39) and speed sensor connector terminal #2. Check for an intermittent open-circuit. Check for an intermittent short-circuit to ground.
Hint: With the control module connected, the ignition on and a voltmeter connected between speed sensor connector terminals #1 and #2 (control module side), the voltage should be approximately 1-3 V below Ubat.
Remedy as necessary.
Other information
- To connect the breakout box, see Connecting the breakout box, 4T65EV-GT Connecting the Breakout Box
- To disconnect the control module, see Transmission control module (TCM), replacing, B5254T2, AW50/51 AWD, B5254T2, AW55-50/51SN Service and Repair
- For information about signals, see Signal specification, 4T65EV-GT Signal Specification
- Checking wiring and terminals Checking Wiring And Terminals
Continue - Fault-tracing information
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Fault-tracing information
Information
Fault-tracing information
If the fault is intermittent, do not verify fault-tracing if the fault does not recur.
It is possible to view the information again, or leave fault-tracing for this diagnostic trouble code (DTC).
Do you want to view the information again?
Yes - Attempt New Test
No - Exit fault-tracing
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Attempt New Test - Checking the transmission output speed sensor signal
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