2007 Toyota Avalon P0500

Had a 2007 Toyota Avalon brought into the shop displaying an ABS light. After performing a road test, I noticed that the speedometer was mostly inoperative. It would bounce up and down erratically, but then later the speedometer would do nothing at all. I scanned for diagnostic trouble codes, and a P0500 (vehicle speed sensor) was registered in the powertrain control ECU. Here's a pic of the warning light on the instrument cluster:

The ABS ECU would not respond whatsoever to an attempted trouble code scan. This was the first indication that the ABS ECU was bad. After disconnecting the ABS ECU harness connector, the speedometer stopped its erratic operation. This was a second indication that the ABS ECU was defective. After confirming that the ABS ECU was receiving battery voltage at the harness connector, and a good ground, the ABS ECU was condemned. Here's a pic of the ABS ECU with the harness connector removed:

The hydraulic ABS actuators and the ABS computer are all built into one integral unit. To remove the ABS ECU (electronic control unit), the brake lines had to be removed from the ABS ECU. Once the brake lines were removed, brake fluid leaked everywhere, so if you are tackling this same job, it wouldn't be a bad idea to have a catch pan under the car before removing the ABS ECU. Also, the use of a line wrench instead of an open end wrench will assist with easily removing the brake lines from the ABS ECU.

Remove the 3 bolts holding the ABS ECU to the body of the car, and the ABS ECU can be wiggled past all of the brake lines.

Once the new ABS ECU is installed into the vehicle, you will need an assistant to help pump the brakes to bleed all of the air out of the brake system. On this vehicle, I initially snugged all of the brake lines into the ABS ECU, and then cracked them open to bleed the air out one by one, as an assistant pumped the brakes for me. Luckily for me, the air bled out quickly. (For the replacement of some ABS modules, the air can be really tricky to get out of the system.)

Upon intial startup of the vehicle after the ABS ECU replacement, the ABS light immediately cleared. I didn't even have to clear it with a scan tool. A post repair road test revealed that the ABS was functioning normally after ABS ECU replacement. Case closed on this Avalon.