C0668: Right Rear Wheel Speed Sensor B Circuit Low

What it means

Right Rear Wheel Speed Sensor B Circuit Low: the signal voltage is below the expected range. Wheel-speed signals feed ABS, ESC, traction control and the speedometer.

At a glance

• Usually lights the ABS or stability-control warning light
• The engine or gearbox may go into limp mode

How it works

The right rear wheel speed sensor B circuit carries that wheel's speed signal to the ABS control module for ABS, stability, and traction functions. This code sets when the module sees the circuit signal below its expected range, which can happen if the signal wire is grounded or a corroded connection restricts it.

Common causes

Most likely first.

1. Signal wire shorted to ground
2. Connector pins corroded - high contact resistance
3. Harness chafing through insulation

Symptoms

• ABS warning light on
• ESC/stability control deactivated
• Possible reduced brake assist
• Speedometer may behave erratically

How to diagnose it

1. Save freeze-frame data and compare all four wheel-speed readings in live data to see whether right rear sensor B is consistently low, absent, or affected only while moving.
2. Inspect the right rear sensor B harness where it can chafe, especially near suspension or body contact points.
3. Check the connector pins for corrosion, looseness, or damaged terminals that could raise contact resistance.
4. With the circuit isolated according to the manufacturer's procedure, test the signal wire for an unintended short to ground.
5. If the harness and connector pass, test sensor B and the ABS module circuit using the manufacturer's diagnostic procedure.

Common fixes

• Clean and properly reconnect corroded right rear sensor B terminals if serviceable.
• Repair chafed insulation and any signal wire short to ground.
• Replace damaged connector terminals or the affected harness section.
• Replace sensor B only if testing identifies it as the source of the low signal.

Can I keep driving?

Basic braking may remain, but ABS and stability or traction control may be disabled and the speedometer may behave erratically. Drive gently with extra stopping distance and avoid conditions that require electronic stability assistance.