Diagnostic guide for P0720

Diagnostic Guide for P0720 - Output Shaft Speed Sensor Circuit Malfunction

The P0720 code indicates a malfunction in the Output Shaft Speed (OSS) Sensor circuit, which is crucial for the Powertrain Control Module (PCM) to monitor vehicle speed and control transmission behavior. The goal of this diagnostic guide is to identify the root cause of the issue, whether it's a faulty sensor, wiring problem, or PCM failure.

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Difficulty

Intermediate

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Estimated Time

30-60 Minutes

Estimated Diagnostic Cost

$0-$100

Typical shop charge to perform this diagnostic process. Repair parts and labor are not included.

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Tools Needed

OBDII scanner, multimeter, wiring diagram, basic hand tools

Safety Notes

Ensure the vehicle is on a flat surface and securely lifted if needed. Be cautious of moving parts and hot engine components during the inspection.

Step 1

Check OBDII Codes

Instruction Connect an OBDII scanner to the vehicle's diagnostic port and retrieve any stored trouble codes.

Expected result Confirm that P0720 is present along with any other related codes.

If Pass If P0720 is the only code, proceed to the next step. If there are additional codes, investigate them as they may provide further insight.

If Fail If no codes are present, ensure the scanner is functioning correctly and the vehicle's ignition is in the ON position. Recheck connections and try again.

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Step 2

Inspect OSS Sensor and Wiring

Instruction Locate the Output Shaft Speed Sensor and visually inspect it and its wiring for any signs of damage, corrosion, or loose connections.

Expected result The sensor and wiring should be intact with no visible damage.

If Pass If everything appears in good condition, proceed to test the sensor's electrical output.

If Fail If any damage is found, repair or replace the wiring or sensor as necessary.

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Step 3

Test OSS Sensor Output

Instruction Using a multimeter, measure the voltage output of the OSS sensor while the vehicle is in motion or while manually rotating the output shaft.

Expected result The sensor should produce a voltage signal that varies with speed.

If Pass If the sensor outputs a proper signal, the sensor is functioning correctly. Proceed to check the PCM.

If Fail If there is no output or the signal is inconsistent, the OSS sensor may be faulty and should be replaced.

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Step 4

Check Electrical Connections

Instruction Inspect the electrical connector at the OSS sensor and the PCM for corrosion, bent pins, or poor connections.

Expected result Connectors should be clean and securely attached with no signs of wear.

If Pass If connections are good, proceed to test the wiring continuity between the OSS sensor and the PCM.

If Fail Clean or repair any corroded or damaged connectors and retest the system.

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Step 5

Test Wiring Continuity

Instruction Using a multimeter, perform a continuity test on the wiring between the OSS sensor and the PCM to ensure there are no breaks or shorts.

Expected result Continuity should be present without any shorts to ground or other circuits.

If Pass If continuity is confirmed, the wiring is intact. The issue may lie within the PCM.

If Fail If there is no continuity or a short is detected, repair the wiring as needed.

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Step 6

Check PCM Functionality

Instruction If all previous tests pass, check the Powertrain Control Module (PCM) for proper operation and any potential software updates.

Expected result The PCM should be functioning correctly without any internal faults.

If Pass If the PCM is operational, consider further diagnostics or consult a professional for advanced troubleshooting.

If Fail If the PCM is found to be faulty, replacement or reprogramming may be necessary.

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