P21C9

What it means

SCR control module power-relay control line stuck high. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.

Is it safe to drive?

The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical.

Most likely causes

• Short to B+

  high

  One of the most commonly reported causes for this code — check this first.

• Connector pins corroded - high contact resistance

  low

  Less common, but worth ruling out after the more likely causes.

• Supply wire pinched against B+ source

  low

  Less common, but worth ruling out after the more likely causes.

Related help

• Full P21C9 diagnosis, causes & costs
• How to read check engine light codes
• Is it safe to drive with the light on?