Chevrolet P1682 Code: Ignition 1 Switch Circuit 2
The engine computer's two ignition power feeds disagree, which can cause stalling or Reduced Engine Power.
Stop driving
Treat this as a stalling risk: the engine can cut out or lose power without warning, which is dangerous on highways or in intersections. Limit driving to short, low-speed trips until the power feed fault is found and repaired.
At a glance
Severity: High
- Meaning
- Ignition 1 Switch Circuit 2
- System
- ECU & Outputs · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $0–$900
- DIY difficulty
- Moderate
On many newer Chevrolets, including the 2008–2012 Malibu, the Cobalt and HHR, the Equinox and the Traverse, the engine control module receives ignition voltage on two separate circuits. One comes through the powertrain relay and its fuse and mainly powers the electronic throttle; the other comes through the run/crank relay and powers the rest of the ECM. P1682 sets when the ECM sees a voltage difference between the two for a moment. Because the throttle feed is safety-critical, a dip there can trigger 'Reduced Engine Power', traction or stability warnings, or even an engine stall. On the Malibu and its platform mates, the most frequent cause is the underhood fuse block itself, where loose terminals or cracked internal connections interrupt one feed, especially when hot.
How to read P1682
- P Powertrain
- 1 Manufacturer-specific
- 6 Computer & outputs
- 82 Specific fault
Symptoms
- Engine stalls while driving or at idle, often restarts after a moment
- 'Reduced Engine Power' message with limited throttle
- 'Service Traction' or 'Service ESC' messages appearing at the same time
- Intermittent crank-no-start, worse in hot weather
- Gauges or warning lights flickering when going over bumps
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Internal fault in the underhood fuse block (loose or fretted terminals, cracked internal connections)
- Failing powertrain relay or run/crank relay
- Loose, corroded or heat-damaged fuse terminals feeding the ECM ignition circuits
- Worn ignition switch or loose connector at the switch
- Poor battery terminal, ground strap or ECM ground connection
- Wiring fault in either ignition feed or ECM connector
Diagnosis step by step
Check battery connections and grounds first
Clean and tighten both battery terminals and check the main ground straps. A loose terminal can make the voltage on one circuit dip enough to set P1682 and throttle codes at the same time.
Tools: Multimeter, Screwdriver
Compare the ignition voltages in live data
With a scan tool, look at the ECM's ignition voltage readings (names vary by model and scan tool). With the engine running they should both show charging voltage, about 13.5–14.5 V, and stay within a few tenths of each other; one that dips or reads lower identifies the weak feed.
Tools: OBD-II scanner
Swap the relays
Swap the powertrain relay and the run/crank relay with an identical relay from the same fuse box and see whether the problem moves or disappears. A cheap relay replacement fixes a significant share of cases.
Tools: Pliers
Wiggle-test the fuse block
With the engine running and the scan tool showing both voltages, gently press on and tap the underhood fuse block and flex the harness under it. A voltage drop, a stumble or a stall while doing so points to an internal fuse block fault.
Tools: OBD-II scanner, Flashlight
Voltage-drop test each feed
Measure the voltage drop from the battery positive to the ECM's ignition input on each circuit with the engine running and loaded (headlights and blower on). More than about 0.3 V of drop on one circuit shows where the resistance is.
Tools: Multimeter
Check the ignition switch and ECM connector
If the fuse block and relays test fine, check the ignition switch output while turning the key slightly in the Run position, and inspect the ECM connectors for pushed-back or corroded pins.
Tools: Multimeter, Flashlight
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean/tighten battery terminals and grounds | Yes | $0–$80 |
| Replace powertrain or run/crank relay | Yes | $15–$90 |
| Replace underhood fuse block | No | $300–$900 |
| Replace ignition switch | No | $150–$450 |
| Repair ECM ignition feed wiring | No | $100–$350 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
P1682 turns on the check engine light, which is an automatic fail at US OBD emissions inspections; intermittent stalling is also a safety concern that should be fixed before a long drive.
Frequently asked questions
Why does my Malibu stall with P1682 when it's hot?
Heat makes loose terminals and cracked connections inside the fuse block or relay expand and lose contact. One ignition feed to the ECM drops out and the engine can stall or go into Reduced Engine Power.
Is it the ignition switch?
Sometimes, but on the Malibu and similar models the underhood fuse block and relays are more common. Test the voltages and swap relays before buying a switch.
Do I need a new fuse block?
If the fault appears when you tap or flex the fuse block, or if one feed drops while the relays are good, the fuse block likely has an internal fault. It's a bolt-in part but must match your vehicle's options.
My Cobalt has P1682 – could it be related to the ignition switch recall?
Cobalt and HHR models were part of GM's widely publicized ignition switch recall, in which the key could slip out of Run. Make sure the recall repair has been done; P1682 can still come from the fuse block or relays even after that.
Sources
- Manufacturer public service information (cross-checked)
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