CARRIER DIAGNOSTIC REFERENCE STATUS LED — TWO-STAGE VARIABLE-SPEED (58MVP / 58MVB / 58UVB) DOC CARRIER-42

Carrier furnace: Code 42 — Inducer Motor Fault

Q: What does code 42 mean on a Carrier furnace?

Code 42 — Inducer Motor Fault. On the two-stage variable-speed control, the inducer did not start within 20 seconds of a call for heat, its RPM is outside the valid range, or the RPM signal was lost for 5 seconds while running. Official checklist: proper vent sizing, restricted combustion air supply, failed inducer motor, improper motor wiring.

YOUR LIGHT: 4 SHORT + 2 LONG FLASHES — MATCH IT ABOVE

Try DIY first, then call a pro

What does code 42 mean on a Carrier furnace? On the two-stage variable-speed control, the inducer did not start within 20 seconds of a call for heat, its RPM is outside the valid range, or the RPM signal was lost for 5 seconds while running. Official checklist: proper vent sizing, restricted combustion air supply, failed inducer motor, improper motor wiring.

GOOD NEWS: THE FIRST CHECKS ARE FREE AND TAKE MINUTES.

Try these first — in this order

Check both terminations outside for blockage. That is the one item on the official list you can do yourself.

1Check: Blocked intake or exhaust termination (snow, leaves, nests) restricting combustion air

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Inducer RPM and wiring diagnosis. The assembly is replaced as a unit. DIY part cost: $250–500 — a pro visit for this class of fault typically runs $150–350.

What causes it (in order of likelihood)

Blocked intake or exhaust termination (snow, leaves, nests) restricting combustion air DIY-CHECKABLE
Failed inducer motor TECH
Loose or incorrect inducer motor wiring TECH
Vent sizing TECH

Parts referenced by this code

Inducer Motor Assembly

$250–500 · Model-specific — match to your unit’s parts list

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Always match parts against your model's parts list — part numbers vary within a series.

Applies to

58MVP (Series 170/180) · 58MVB · 58UVB

Different Carrier generations use different code maps. If your series isn't listed, don't assume this meaning — check your blower-door label.

Verified against Carrier 58MVP/58MVB/58UVB Troubleshooting Guide (58-06T), p.8/28-29 — “INDUCER MOTOR FAULT – Indicates the inducer has not started within 20 seconds after a call for heat, the inducer motor RPM is outside its valid range of operation, or the inducer RPM signal was lost for 5 seconds during operation. Check for: Proper vent sizing. Restricted combustion air supply. Failed inducer motor. Improper motor wiring.”

Verified against Carrier 58MVB Service and Maintenance Instructions (58MVB-2SM), p.18 — “Check for: Proper vent sizing. Failed inducer motor. Restricted combustion air supply. Improper motor wiring.”

Verified against Carrier 59MN7A Troubleshooting Guide (59MN7A-01T), p.9

Last verified 2026-09-05 · how we verify

Related Carrier fault codes

These codes use the same status led — two-stage variable-speed (58mvp / 58mvb / 58uvb) system.

Pattern	Meaning
	Code 41 — Blower Motor Fault
	Code 43 — Low-Heat Pressure Switch Open in High Heat
	Code 32 — Low-Heat Pressure Switch Did Not Close or Reopened
	Code 25 — Model Selection or Setup Error

See all Carrier furnace fault codes →