P1682 Code: Voltage Difference Between the Module Two Ignition Feed Circuits (Manufacturer Code)

What the P1682 code means

The engine control module on many General Motors group vehicles is not powered through a single path. It has two independent ignition circuits, each with its own fuse and its own relay.

That design has a safety reason. One of the circuits feeds the internal components tied to electronic throttle control, specifically, and the other feeds the rest. Since the throttle is a critical system, the module constantly checks that both feeds carry the same voltage.

The P1682 code is stored when that comparison fails: the two inputs do not match. That means one of the two paths is losing voltage or is not arriving at all.

The system response is blunt because it cannot guarantee throttle control with a doubtful supply. The vehicle may refuse to start, go into limp mode or shut off while driving, and that last scenario is what makes this code dangerous.

The causes cluster in the supply path: ignition switch with worn contacts, fuses, relays, connectors and grounds. Installed accessories that intercept the ignition, such as GPS tracker kill switches, also cause it.

It is worth understanding why the manufacturer duplicated this supply instead of reinforcing a single one. The reason is functional safety: in a system with an electronic throttle, a momentary voltage drop in the wrong circuit could leave the module without control over the throttle while everything else keeps working. Splitting the feeds and comparing them lets it detect that condition before anything happens, and respond by cutting out instead of taking a risk.

P1682 code symptoms

• The engine cranks but does not start.
• The engine suddenly shuts off while driving.
• Check engine light on, often after several drive cycles.
• Loss of power or limp mode.
• Intermittent starting that works some times and not others.
• Dash gauges that behave erratically.
• May appear together with system power codes.
• The fault can show up only on a cold start or only with the vehicle hot.

Likely causes of the P1682 code

1. Ignition switch with worn contacts. A very frequent cause in this family of vehicles.
2. Fuse in one of the two circuits blown or making poor contact.
3. Powertrain or start relay with worn contacts.
4. Installed accessories that intercept the ignition, such as GPS tracker kill switches or alarms.
5. Module connector with backed-out pins or corrosion.
6. Weak battery or sulfated terminals.
7. Rusty engine or body grounds.
8. Damaged power wiring or badly made splices.
9. Failed control module. The last possibility.

How to diagnose the P1682 code step by step

1. Ask whether the vehicle has installed accessories such as GPS trackers with a kill switch or alarms. It is a growing cause and easy to rule out by unplugging them.
2. Check the battery and its terminals by measuring voltage at rest and during cranking.
3. Measure the voltage of both ignition circuits at the module connector with the key on. They should match.
4. Check the fuses of both circuits, confirming not only that they are intact but that they make good contact in their sockets.
5. Test the relays involved by swapping them with identical ones if the vehicle allows it.
6. Verify the ignition switch by measuring continuity in its positions while moving the key.
7. Inspect and clean the grounds on the engine and the body.
8. Inspect the module connector for backed-out pins.
9. Wiggle the key in the ignition with the engine running and watch whether the engine stumbles, which points to the ignition switch.

How to fix the P1682 code

• Remove or correct installations of accessories that intercept the ignition circuit.
• Replace the ignition switch if its contacts are worn.
• Replace defective fuses and their fuse holders if the contact is poor.
• Replace relays with worn contacts.
• Clean or replace the module connector and protect it with dielectric grease.
• Correct the terminals, battery and grounds down to bare metal.
• Repair damaged wiring following its original routing and without temporary splices.
• Replace the ignition switch if the engine stumbles when you wiggle the key in the ignition.

Do not keep driving with this code. A sudden shutdown at speed means losing power steering and brake assist all at once.

Technical reference data

• The module receives two independent ignition circuits, each with its own fuse and relay.
• One feeds the internal circuits of the electronic throttle control and the other the rest.
• The code is stored when the module detects a voltage difference between the two.
• Expected voltage on both circuits with the key on: battery voltage, around 12 volts.
• It can come with other codes that identify which of the two circuits is affected.
• P1xxx codes are reserved for each manufacturer.
• The duplicated supply responds to the functional safety of the electronic throttle.

Brand-specific notes

GPS trackers with kill switches wired into the ignition circuit are an increasingly common cause of this code, especially on financed or fleet vehicles. Temporarily disconnecting that accessory is a five-minute test that rules the suspicion in or out without taking anything apart.

The ignition switch is the classic suspect. Its internal contacts wear with the years and start feeding one circuit worse than the other, which is exactly what this code describes.

P1682 on General Motors Vehicles

The module is powered by two independent ignition circuits and compares their voltages, so a difference between them sets this code.

Frequently asked questions about P1682