P2506

What it means

The switched-battery input to the ECM/PCM is present, but the level or transient behaviour is out of plausibility — sagging during cranking, slow ramp-up after main-relay close, or noisy. Often caused by aged main relay contacts or a weak battery feed under load.

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

• Aged main relay contacts with rising contact resistance

  high

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

• Weak battery sagging during crank

  medium

  A plausible cause — test and verify before replacing parts.

• Sensor element aged beyond calibration window

  low

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

Related help

• Full P2506 diagnosis, causes & costs
• How to read check engine light codes
• Is it safe to drive with the light on?