Honda / Acura Fault Codes (OBD1 PGM-FI)

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Note: This page may contain community-sourced information and/or data from manufacturer manuals. Descriptions, probable causes, and default actions can vary by year or ECU calibration and may include inaccuracies. Always verify using official manufacturer documentation or trusted service information.
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Honda / Acura — OBD1 (PGM-FI) Blink codes • 1990s

Code	Description	Info
0	ECU / ECM fault (control unit / ROM)	↗ Sources: Honda service refs; HA Motorsports.
1	O2 Sensor #1 (Heated, primary) — circuit fault	↗ Sources: HA Motorsports; Eddie Abbondanzio.
2	O2 Sensor #2 (secondary) — circuit fault (where fitted)	↗ Source: HA Motorsports.
3	MAP sensor — fault	↗ Sources: HA Motorsports; Honda PGM-FI refs.
4	CKP — crankshaft position sensor (distributor) fault	↗ Sources: HA Motorsports; Honda PGM-FI refs.
5	MAP sensor — fault (alt. mapping; some ECUs use 3 & 5)	↗ Source: HA Motorsports.
6	ECT — engine coolant temp sensor fault	↗ Sources: HA Motorsports; Eddie Abbondanzio.
7	TPS — throttle position sensor fault	↗ Sources: HA Motorsports; Eddie Abbondanzio.
8	TDC — top dead center sensor (distributor) fault	↗ Sources: HA Motorsports; Eddie Abbondanzio.
9	CYP — #1 cylinder position sensor (distributor) fault	↗ Sources: HA Motorsports; Eddie Abbondanzio.
10	IAT — intake air temperature sensor fault	↗ Sources: HA Motorsports; Eddie Abbondanzio.
11	Engine overheating (note: Hondata S300 specific on some lists)	↗ Stock ECUs rarely use 11; Hondata may set it for high ECT. Source: Eddie Abbondanzio (notes).
12	EGR lift valve — fault (where equipped)	↗ Source: HA Motorsports.
13	BARO — barometric pressure sensor fault	↗ Sources: HA Motorsports; Honda PGM-FI refs.
14	IACV / EACV — idle air control valve fault	↗ Sources: HA Motorsports; Honda PGM-FI refs.
15	Ignition output signal fault	↗ Source: HA Motorsports.
16	Fuel injectors — circuit fault	↗ Source: HA Motorsports.
17	VSS — vehicle speed sensor fault	↗ Source: HA Motorsports.
19	A/T lockup control valve (auto trans)	↗ Source: HA Motorsports.
20	ELD — electrical load detector (alternator load sense)	↗ Sources: HA Motorsports; Honda PGM-FI refs.
21	VTEC solenoid (spool) — circuit fault	↗ Sources: HA Motorsports; Eddie Abbondanzio.
22	VTEC pressure switch — fault	↗ Sources: HA Motorsports; Eddie Abbondanzio.
23	Knock sensor — fault (common on B/D-series swaps)	↗ Sources: HA Motorsports; Eddie Abbondanzio.
30	AT FI signal A (auto trans equipped models)	↗ Sources: HA Motorsports; Honda PGM-FI refs.
31	AT FI signal B (auto trans equipped models)	↗ Sources: HA Motorsports; Honda PGM-FI refs.
36	Traction control (some JDM ECUs) — fault detected	↗ Source: HA Motorsports (JDM note).
38	Secondary VTEC solenoid (3-stage D15B JDM P2J) — fault	↗ Source: HA Motorsports (JDM note).
41	Primary O2 heater — circuit fault (HO2S heater)	↗ Sources: HA Motorsports; Eddie Abbondanzio.
43	Fuel supply / fuel system — out of range	↗ Sources: HA Motorsports; Eddie Abbondanzio.
45	Fuel system — rich/lean malfunction (overall)	↗ Source: HA Motorsports.
48	LAF — lean air-fuel sensor (some VTEC models)	↗ Source: HA Motorsports.
54	CKF — crank fluctuation sensor (some OBD1 late / OBD2-crossover)	↗ Appears on some late OBD1/early OBD2 systems. Source: HA Motorsports.
58	TDC sensor #2 (where applicable)	↗ Source: HA Motorsports.
61	Primary O2 sensor — circuit fault (signal)	↗ Source: HA Motorsports.
63	Secondary O2 sensor — circuit fault (signal)	↗ Source: HA Motorsports.
65	Secondary O2 heater — circuit fault (heater wiring)	↗ Source: HA Motorsports.
67	Catalytic converter efficiency fault (where fitted)	↗ Source: HA Motorsports.
71	Random misfire — Cylinder 1 (late OBD1 / early OBD2 overlap)	↗ Model-dependent; many are OBD2. Source: HA Motorsports.
72	Random misfire — Cylinder 2	↗ Source: HA Motorsports.
73	Random misfire — Cylinder 3	↗ Source: HA Motorsports.
74	Random misfire — Cylinder 4	↗ Source: HA Motorsports.
80	EGR valve / passages — fault (varies by model)	↗ Source: HA Motorsports.
86	ECT / cooling system — overheat logic (model dependent)	↗ Source: HA Motorsports.
91	Fuel tank pressure sensor — fault (evap)	↗ Source: HA Motorsports.
92	EVAP solenoid / valve / vacuum lines — fault	↗ Source: HA Motorsports.