P1682 Code: Ignition 1 Switch Circuit 2 Malfunction (GM Diagnosis & Repair Guide)

P1682 is a GM-specific electrical code that causes some of the most frustrating intermittent no-start complaints on the road. The good news is that it's almost never the ignition switch itself — it's usually the underhood fuse block or a relay.

What P1682 Means

P1682 is defined as "Ignition 1 Switch Circuit 2 Malfunction." The ECM receives two separate ignition voltage feed circuits — one through the powertrain relay (which powers throttle actuator control circuits), and one through the run/crank relay. This code sets when the ECM detects a voltage difference between the two circuits greater than roughly 3 volts.

Symptoms of P1682

• Intermittent no-start or crank/no-start condition
• Stalling while driving
• Check engine light illuminated
• Flickering gauges or radio glitches
• Engine may crank but fail to start

Common Causes of P1682

• Corroded or loose connections at the underhood fuse block (UBEC) — the overwhelming majority of cases
• Failed ignition relay or run/crank relay
• Blown fuse
• Damaged wiring or connector (commonly at the ECM connector, e.g., connector X3, pin H6)
• Faulty ignition switch (less common on newer relay-based GM systems)
• Low battery voltage or charging system issues

GM Vehicles Affected by P1682

P1682 has been widely reported across the GM lineup from roughly 2007-2021, especially on the Chevrolet Silverado, Traverse, Cruze, and Impala; GMC Sierra and Acadia; and Buick Enclave.

How to Diagnose P1682

1. Retrieve the code and check battery state of charge and charging voltage.
2. Inspect the underhood fuse block for visible corrosion, melted plastic, or water intrusion.
3. Test the ignition relay and run/crank relay — swap in a known-good relay to confirm.
4. Check voltage at both ignition circuits at the ECM connector with the key on; readings should be within about 0.5V of each other.
5. Inspect connector terminals for corrosion, especially at harness pass-through points prone to water intrusion.

Step-by-Step Repair for P1682

1. Retrieve the code and verify battery voltage and charging system health.
2. Inspect the underhood fuse block for corrosion, melting, or water intrusion.
3. Test the ignition and run/crank relays by swapping in known-good units.
4. Check voltage at the ECM connector on both ignition circuits and compare readings.
5. Clean and repair any corroded connector terminals found.
6. Replace the faulty relay, or the underhood fuse block (UBEC) assembly if internal circuit damage is found.
7. Clear codes and verify consistent cranking/starting over multiple cycles, including hot and cold starts.

OEM Part Numbers (Representative — Confirm for Your VIN)

• Ignition/run-crank relay: GM #13595908 — approx. $15-$30
• Underhood fuse block (UBEC), updated design: GM #84303175 — approx. $250-$400
• Battery terminal/pigtail repair kits: approx. $20-$40

Labor Time

• Relay replacement: ~0.3 hour
• UBEC/fuse block replacement (including re-pinning connectors): 1.5 – 3.0 hours
• Wiring repair: 1.0 – 3.0 hours depending on access

Estimated Repair Cost for P1682

• Relay fix: $50 – $100
• UBEC replacement: $350 – $650
• Wiring repair: $150 – $450

Frequently Asked Questions

Is P1682 usually the ignition switch itself?

No — despite the name, the actual ignition switch is rarely the cause on newer relay-based GM systems. The underhood fuse block and its relays are responsible for the vast majority of cases.

Why is this code so hard to diagnose?

Because it's often intermittent — corrosion or a marginal connection can pass a voltage test one moment and fail the next, especially after the vehicle heats up or hits a bump. Comparing voltage at both ignition circuits during an active fault is the most reliable way to catch it.

Can a weak battery trigger a P1682 code?

Yes. Low battery voltage or a struggling charging system can create enough of a voltage discrepancy between the two ignition circuits to set the code, so it's always worth ruling out battery health before chasing wiring issues.

What's the cheapest fix to try first?

Swapping in a known-good relay is quick, inexpensive, and rules out one of the most common causes before you invest time in inspecting the fuse block or wiring harness.

Since this code often shows up as an intermittent no-start, having a reliable jump starter on hand for diagnosis and roadside situations is essential. The Buture Beta09 8000A Jump Starter with 160 PSI Air Compressor is a strong match for this kind of diagnostic and roadside work. Shop more GM parts and accessories at www.gmserviceguy.shop.

Repair costs and labor times are estimates based on average national rates and can vary by region, shop, vehicle model year, and mileage. Always confirm exact OEM part numbers for your specific VIN before ordering.