P1682
Ignition 1 Switch Circuit 2 (Driver 5 Line 2)
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The P1682 code is a GM-specific code that indicates a voltage difference between two ignition 1 power supply circuits feeding the PCM. The PCM receives ignition voltage through two separate paths — one through the powertrain relay and one through the run/crank relay. When the voltage difference between these two circuits exceeds the programmed threshold, the PCM sets this code.
On GM trucks and SUVs (Silverado, Sierra, Trailblazer, Envoy, etc.), this code is notoriously associated with the underhood fuse box. Inside the fuse box, small solid copper traces route power between fuses and relays. These traces are known to crack — especially at sharp bends — creating an open or high-resistance connection in one of the ignition circuits. The result can range from intermittent no-start conditions to a completely dead vehicle.
The ignition switch itself is another common culprit. On many GM vehicles, the electrical portion of the switch can be replaced separately from the lock cylinder, making it a relatively affordable repair. Diagnosis involves measuring voltage at both ignition 1 circuits at the PCM connector with the key in the run position — they should be nearly equal. If one is significantly lower, trace that circuit back through its fuse and relay to find the failure point.
Severity
Symptoms
- •Engine cranks but will not start (no-start condition)
- •Intermittent starting problems that come and go
- •Dashboard warning lights flicker or dim unexpectedly
- •Battery seems to drain overnight or between starts
- •Headlights may dim during cranking
Likely Causes
The ignition switch is not properly delivering voltage to one of the two ignition 1 circuits, causing a voltage difference that exceeds the PCM's allowable threshold. This is the most common cause.
The underhood fuse box on many GM trucks and SUVs has thin solid wire traces inside that are prone to cracking — especially at 90-degree bends. This is a notorious failure point that interrupts the ignition circuit.
A blown fuse in either the powertrain relay or run/crank relay circuit can cause a voltage difference between the two ignition 1 supply paths to the PCM.
Corrosion or loose pins at connectors in either ignition 1 circuit — particularly at the fuse box, relays, or PCM connector — create high resistance and voltage drops.
One of the relays supplying voltage to the ignition 1 circuits has failed, cutting power to one of the two paths and creating the voltage difference.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace the ignition switch (electrical portion)
- Inspect and repair or replace the underhood fuse box if traces are cracked
- Check and replace blown fuses in the ignition 1 circuits
- Clean corroded connections at relays, fuse box, and PCM connectors
- Test and replace the powertrain relay or run/crank relay if failed