P0503 is a diagnostic trouble code that stands for “Vehicle Speed Sensor Intermittent/Erratic/High.” It is a common error code for vehicles made since 1996. Read to know more about the P0503 error code.
P0503 is a generic trouble code, which means it applies to any vehicle manufactured from 1996 to the present. You’ll notice it, particularly in those equipped with an OBD-II system, such as those found in Cadillac, Chevrolet, GM, GMC, Saab, Subaru, and Volvo. Do keep in mind that troubleshooting and repairs differ from one another.
What is P0503?
The PCM (powertrain control module, ECM, or engine control module in other vehicle makers) has identified an irregular, intermittent, or excessive voltage input signal from the VSS when error code P0503 is saved (vehicle speed sensor). The “A” in ‘Vehicle Speed Sensor A Intermittent’ refers to the primary VSS in a system made up of numerous vehicle speed sensors.
Electromagnetic speed sensors are standard on most automobiles. A toothed reluctor ring wheel or gear attached to an axle, transmission/transfer case output shaft, driving shaft, or differential gear is used in this form of sensor. The reluctor device spins with the shaft pins, connecting to the stationary electromagnetic sensor.
When the reluctor passes very close to the sensor’s electromagnetic tip, the notches in the reluctor ring cause disruptions in the sensor circuit. The PCM and other controllers receive combinations of these circuit completions and other disruptions as waveform patterns that represent voltage.
Source : StandardBrand
The PCM uses data from one or more vehicle speed sensors to monitor the vehicle’s speed and compare it to inputs from the ABCM (antilock brake control module) or EBCM (electronic brake control module) (electronic brake control module).
A secondary VSS input may be monitored using one or more wheel speed sensors in various vehicle makes and models, but the primary VSS input (A) is most often initiated by the transmission’s VSS. If the primary VSS detects intermittent, irregular, or high input voltage, the Check Engine light will illuminate, and the error code P0503 will be stored in the vehicle’s memory.
Symptoms
- Check Engine Light on
- The speedometer needle may swing up and down
- Broken speedometer
Causes
- A malfunctioning car speed sensor
- Damages to wiring or connectors in the vehicle speed sensor circuit
- Several defective wheel speed sensors and hub bearings
- Broken ABS tone rings
- An inaccurate ECM
- Incorrect wheel or tire size
- Instrument cluster failure
How to diagnose P0503 like a pro
Prep
You will need a DVOM (digital volt-ohmmeter), an oscilloscope, and a vehicle information source to diagnose this code. Begin your diagnosis by visually inspecting the wiring system, connectors, and speed sensors. As needed, repair open or short circuits and clear excessive metallic debris from impacted sensors. When inspecting the sensors, also check the condition of the reluctor ring.
Diagnosis
Connect the scanner to the vehicle’s diagnostic connection to get all stored trouble codes and accompanying freeze-frame data. Write down all of the information before clearing the codes. Search for the applicable TSB using your vehicle information source (technical service bulletins). To match the information, use your vehicle’s symptoms.
During your test drive, use the scanner data to monitor both wheel speed and vehicle speed. You can restrict the data stream to display only the relevant fields and improve the speed and precision with which the data is delivered. If you see unpredictable or inconsistent readings from the VSS or wheel speed sensors, the issue could be with the wiring, electrical connector, or sensors.
Locate the VSS circuit from where the low voltage input is coming, and then use the DVOM to carry out a resistance test on the required sensor. For manufacturer-specific suggestions, check your vehicle’s information manual. Sensors that do not meet the standards must be replaced.
Using the oscilloscope, probe the sensor signal and ground wires to obtain data from each individual VSS. To successfully execute this test, you may need to jack or raise the car. Run up the drivetrain while viewing the waveform pattern on the oscilloscope after the drive axle/s have been safely secured off the ground. Take note of any flaws or inconsistencies in the pattern and proceed with the diagnostic if needed.
Wheel speed sensors and sensor wiring harnesses can be damaged during brake repairs, and vehicle speed sensors can be damaged during routine maintenance. If this code appears during a repair, suspect a faulty sensor, connector, or harness.
Possible fixes for a P0503 error code
- Changing the speed sensor
- Repairing or replacing the speed sensor circuit wiring or connectors
- Changing out one or more wheel speed sensors
- Changing a hub bearing
- Replacing the ECM after replacing a CV axle due to a defective tone ring
- Instrument cluster replacement
- Adding the proper wheels and tires to the vehicle
How serious is the P0503 error code
The P0503 error code is not serious. It only impacts the car’s speedometer performance. The only issue that could arise while driving with a P0503 code is a speeding ticket.
Cost of diagnosing the P0503 error code
The P0503 code diagnosis costs 1 hour of labor. The cost of auto repair labor varies according to region, vehicle make and model, and even engine type. The average auto repair shop charges anywhere between $75 and $150 per hour.
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