P1682

Ignition 1 Switch Circuit 2

Car Fault Codes GMC Engine computer & electrical

Can you still drive? With care, short trips only

Who can fix it? Needs a workshop

Typical repair time 30 minutes – 3 hours

Typical cost SAR 50 to 800

What it means

This is a GMC manufacturer-specific code, and the same number can mean something different on other makes. The engine computer monitors two separate ignition signals from the ignition switch, and it sets this code when the voltage on the second one differs from the first. The cause is usually in the feed path itself, such as a fuse, a corroded terminal or an aftermarket electrical add-on, not the computer.

Models covered: GMC models, mainly around 2000–2007 (e.g. Sierra, Yukon).

Symptoms4

Intermittent stalling, especially over bumps or with vibration.
No start at times, then it starts on a later try.
Check engine light on, sometimes with other voltage codes.
Odd dashboard behavior at the moment the fault occurs.

Possible causes6

Aftermarket add-ons tapped into the ignition feed causing voltage drop or a blown fuse.
A fuse with poor contact or blown in the second feed circuit.
Corroded fuse block terminals or engine computer connector.
A faulty electrical ignition switch in the steering column.
Poor battery terminals or a weak ground.
An engine computer fault (rare).

How to diagnose5

Check for any add-ons connected to ignition feeds and disconnect them temporarily.
Measure both ignition feed voltages at the computer while running and compare them.
Check fuses and their terminals in the block by measuring, and look for heat marks.
Check the battery terminals and main ground.
Gently wiggle the wiring and ignition switch while monitoring to find an intermittent break.

How to fix5

Remove the aftermarket add-on or rewire it correctly with its own fuse.
Replace the damaged fuse and repair the block terminals.
Clean and tighten the battery terminals and ground.
Replace the electrical ignition switch once testing confirms it is at fault.
Clear the codes and drive on varied roads to confirm the code does not return.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low for a fuse, terminal or removing an add-on, and higher for an ignition switch or hidden wiring repair.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

I added accessories to my Sierra. Could they cause this code?

Possibly. Lights or devices tapped into ignition feeds without their own fuse and relay can pull voltage down or blow a fuse, making the two circuits differ.

Why does the engine stall only over bumps?

A loose terminal or poorly seated fuse breaks contact for a moment with vibration, so the computer briefly loses the ignition signal.

Does the engine computer need replacing?

Very rarely. Most cases are solved at the fuses, terminals and ignition switch.

Was this explanation helpful?

Tap the stars to rate; you can change it later.

This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

Report a mistake

Spotted something inaccurate? Tell us and we will review and correct it.