Engine controls ignition relay codes

How its codes differ

• P1682 (GM: Ignition 1 Switch Circuit 2) sets when the two ignition voltage feeds the engine computer compares differ by more than about 3 volts. A failing ignition relay is the documented cause on several GM bulletins, after the circuits test good.
• When P1682 is stored with P0689 or P0101 on some GM trucks and SUVs, a relay or fuse block terminal problem can be the real fault; GM notes MAF sensors replaced for P0101 when it was not.
• GM bulletins for the 2014 Silverado 1500, Sierra 1500 and Impala describe an intermittent crank or no-start with P1682 traced to the engine controls ignition relay.

Codes

• P1682

  Engine computer’s two ignition voltage feeds disagree (GM)

  Severity: Inspect soon

Signs it's failing

• Check engine light with P1682, sometimes with P0689
• Intermittent crank or no-start
• Reduced engine power or stalling

How to test it

1. Have the battery and charging system tested first; a weak battery or battery drain can also set P1682. (Low risk)

2. Read all stored codes with a scan tool and ask a GM dealer whether a bulletin for P1682 applies to your VIN. (Low risk)

3. Testing the relay terminals, ignition feedback circuit and relay control circuit, or swapping in a known-good identical relay, is a job for a shop. (Best left to a shop)

   Warning: Swapping relays when a short is present can damage the good relay, and back-probing fuse block and engine computer circuits can cause further damage. Leave it to a shop.

After the repair

• Confirm the engine starts reliably over several days.
• Clear codes only after the repair and confirm P1682 does not return.