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SPN 3965moderate severity✨ AI-generated

Park Brake Control Signal Circuit Low

The park brake control signal circuit is reading a low voltage condition.

Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.

What it means (plain English)

The computer thinks the signal from the park brake control is too low, which can mean a problem with the wiring or the switch itself.

What the computer is actually seeing

The vehicle's computer expects to see a voltage between 0.5V to 5.0V when the park brake is engaged. When the signal drops below 0.5V, it triggers this code.

What a healthy reading looks like

Expected voltage for a properly functioning park brake signal is 0.5V to 5.0V when the brake is applied.

Guided diagnostic — the DiagCoach way

Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.

  1. 1Inspect the wiring and connectors going to the park brake switch for any visible damage or corrosion.
  2. 2With the park brake engaged, use a multimeter to check the voltage at the switch; it should be between 0.5V and 5.0V.
  3. 3If the voltage is low, trace the wiring back for damage; if intact, test or replace the park brake switch.

Common causes

  • Damaged wiring or connectors in the park brake circuit
  • Faulty park brake switch
  • Corrosion in the connectors

Typical repair cost

$$$

Related codes

Frequently asked questions

Is it safe to drive with this code?

It's generally drivable but be sure your park brake works as intended; don't ignore it.

Will this code come back if I clear it?

If the underlying issue isn't fixed, yes, it will likely return.

Why do I see this code pop up with SPN 703?

SPN 703 often pairs with park brake issues; it relates to the brake system and can indicate a common fault.

Working a real vehicle right now?

Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.

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