Sensor Reference Voltage "A" Circuit/Open

What it means

The 5-volt reference supply that the ECU sends to a group of sensors is out of range. Because several sensors share it, one shorted sensor can pull the whole circuit down and cause several codes at once.

Symptoms

• Check engine light on
• Several sensor codes at once
• Limp mode
• No-start in some cases

Probable causes

Most likely first

1. 1A shorted sensor on the 5V reference circuit
2. 2Wiring chafed and shorted to ground
3. 3ECU fault (rare)

How to diagnose it

Work through these in order before buying parts

1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
2. 2Note which other sensor codes are set; they share the reference.
3. 3Unplug sensors on the circuit one at a time while watching the reference voltage. When it recovers, the last sensor unplugged is the culprit.
4. 4Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

• Replace the shorted sensor
• Repair the wiring