VSC Light, C1422 | Toyota RAV4

VSC Light turns on when you press on the brake pedal.
Code in ABS Module
- C1422 Master Cylinder Pressure Sensor Zero Point High Malfunction

When the stop light switch is OFF, the PMC terminal voltage is more than 0.86 V for 5 seconds or more.
Possible Causes
- Stop light switch
- Stop light switch circuit
- Master cylinder pressure sensor circuit
- Brake actuator assembly (Master cylinder pressure sensor)

First, I’ve verified that the Stop Light Switch works ok.
- Checked for a faulty or misadjusted stop light switch.
Hooked up my scanner and monitored the live data in the VSC system
- Any time I step on the brake the Stop Light Switch input should turn ON before the Master Cylinder Pressure Sensor reads higher than 0.836 volts. Basically it means that if pressure sensor detects that i step on the brake pedal, the brake pedal switch should also indicate that, in correlation.
My scanner had PIDs for two brake switch inputs (terminals STP & STP2 at ABS Unit).
- When I pressed on brake pedal, both of them should indicate ‘ON’, but in my case only one of them indicated ‘ON’.
- The missing stop signal came from a STP terminal signal, which path lies through the Brake Relay (left side of engine) and into the Stop Light Control Relay (above right kick panel).
So, I decided to check the Stop Light Control Relay and see if it outputs any voltage when I step on the brake pedal.
- Location of Stop Light Control Relay
When I found it, it had signes of water damage

According to my research, water intrusion is a common issue on Toyotas like ~2010 RAV4, ~2013 Highlander …

To prevent same issue from happening again, I asked the customer to deal with the source of the water leak before he replaces the relay.

New Stop Light Control Relay fixed the problem.