Working on your car can be satisfying, especially when you’re tackling issues yourself. Modern vehicles, like Toyotas, come equipped with sophisticated onboard diagnostic systems, often referred to as OBD2. When things go wrong with systems like the wheel speed sensors, your OBD2 system will often alert you with a trouble code. Recently, I dove into diagnosing a potential wheel speed sensor problem on a Toyota, and here’s a breakdown of the process, focusing on accessing the sensor and initial tests.
The first hurdle was simply getting to the sensor wires. Initially, it seemed necessary to remove a large interior side panel to gain access. This involved disassembling a significant portion of the interior – a time-consuming and somewhat frustrating task. However, I discovered a potentially simpler approach. It appears that by removing the rear seat and peeling back the carpet, sufficient access to the sensor wiring might be achievable. While not as wide open as removing the entire panel, for those comfortable working by feel, this could save considerable time. I plan to test this theory when reassembling the interior.
For this initial diagnostic session, however, the interior was already partially disassembled. Looking into the rear hatch towards the left side, you can see the access area.
This image, taken from the rear hatch, shows the left side of the interior. The left rear brake light is visible on the left, and the area for the wheel speed sensor is on the right, near the open left rear door.
Getting a closer view, kneeling where the rear seat would normally be and facing the rear of the car, reveals the sensor wiring more clearly. You can see where the wiring comes through from the wheel well and connects to its connector.
With access gained, the next step was to disconnect the sensor connector and measure the sensor’s resistance. Using a multimeter, I measured approximately 1 Kilo-Ohm (KΩ). While the exact specification for a 2002 model year Toyota wasn’t immediately available, referencing the 2005 specification, which ranges from 0.9 to 1.3 KΩ, suggests the sensor resistance is likely within the acceptable range.
To further investigate the sensor’s functionality, I reconnected the connector and employed a vintage piece of diagnostic equipment: a Micronta Transistorized Signal Tracer. This tool, likely dating back to the 1960s or 70s, is essentially an amplifier and speaker with a volume control. Originally designed for tracing audio signals in radios, it can also be adapted for other signal types.
The idea was to use the signal tracer to listen to the signal generated by the wheel speed sensor as the wheel rotates. Wheel speed sensors typically generate a sine wave signal, and the signal tracer should convert this into an audible output. The test proved successful. As the speed increased, both the pitch and volume of the sound from the signal tracer changed accordingly – becoming louder and higher in frequency, as expected from a functioning wheel speed sensor.
However, despite confirming the sensor was producing a signal, the test didn’t reveal any obvious breaks or anomalies in the signal that could explain the original issue. This means there’s no immediate “smoking gun” pointing to a faulty sensor itself.
The next steps involve investigating the right rear sensor for comparison. Accessing this sensor should be simpler, potentially just requiring the removal of the other rear seat. Comparing readings between the left and right rear sensors might reveal further clues. Additionally, clearing the error code for the left rear sensor and observing if it reappears will be crucial.
Finally, a question remains about the symptoms of a cracked tone ring. If the tone ring, which the sensor reads, is cracked but not completely broken, what kind of signal disruption or symptoms would that cause? Understanding this could be the key to diagnosing the underlying problem.
