Underhood fuse block (engine compartment fuse box) codes

The underhood fuse block, also called the engine compartment fuse box or battery junction box, holds the fuses and many of the relays that feed engine circuits such as the engine computer, fuel injection and ignition. Its connectors and terminals carry high current, so heat, corrosion or water inside the box can cut or disturb power to several systems at once.

How its codes differ

  • P1682 with P0689 on 2013–2017 Traverse, Acadia and Enclave can come from arcing or corrosion at one terminal of a fuse block connector, causing reduced power or a stall. GM also names fuse block terminals for P1682 on 2019–2020 heavy-duty trucks and SUVs.
  • C0020 with U3003 on 2020–2021 Ford Super Duty trucks is linked to water in the battery junction box, often with other electrical faults at the same time.
  • When several electrical faults appear together, as in the Ford Super Duty bulletin, a shared power feed such as the fuse block is worth checking before individual parts are replaced.

Codes

  • P1682

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

    Inspect soon

Signs it's failing

  • Check engine light with P1682 and/or P0689 (GM crossovers and trucks)
  • Reduced engine power message or stalling
  • Several electrical faults or warning lights at once
  • ABS light with C0020 and U3003 (Ford Super Duty)

How to test it

  1. With the ignition off, open the fuse block cover and check that it was fully closed and its tabs are intact. Look for water, green or white corrosion, or melted or darkened plastic around connectors. Do not pull wiring or probe terminals. (Low risk)

  2. Check any fuse named on the cover for the circuit that stopped working; the cover shows each fuse's location and rating. (Low risk)

  3. Ask a dealer whether a bulletin applies to your VIN before the engine computer or sensors are replaced. (Low risk)

  4. Repairing fuse block terminals, testing circuits and replacing the fuse block are jobs for a shop. (Best left to a shop)

    Warning: The fuse block is connected directly to the battery and carries high current; a slip can cause sparks, burns or further damage. Leave terminal and circuit work to a shop.

After the repair

  • Confirm the fuse block cover is fully seated and latched so water cannot get in.
  • Clear codes only after the repair and confirm they do not return after several drives.

Sources and review

  1. Owner's Manual: Checking Fuses (Honda publication A3BM2626IOM) — American Honda Motor Co.
  2. GM PIT5643: P0689 and/or P1682, arcing or corrosion at X3 terminal 51 of the underhood fuse block (2013–2014 Enclave, Acadia, Traverse) — General Motors / NHTSA ,
  3. GM bulletin 19NA276: reduced engine power and/or stall with P1682 and/or P0689 (2013–2017 Enclave, Traverse, Acadia) — General Motors / NHTSA ,
  4. GM PIP5729: SES lamp with P1682 (Ignition 1 Switch Circuit 2) (2019–2020 HD trucks, Tahoe, Suburban, Yukon, Escalade) — General Motors / NHTSA ,
  5. DTC P0685, P0689, P0690 or P1682 (LFW), 2011 Saab 9-4X service information — Saab Automobile / General Motors (Saab WIS online archive)
  6. Ford TSB 21-2176: engine will not turn off and electrical faults, ABS lamp with C0020 and U3003, battery junction box water intrusion — Ford Motor Company / NHTSA ,
Last reviewed
Written by
Saurabh K.
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