Fault Codes Explained

This page explains what each of the PGM-Fi fault codes means, the implications on operation of the ECU when running under the fault condition, and comments on typical causes for the fault.

To read how to obtain fault codes from your vehicle, please take a look here.

If you have any corrections with the details held here or have the description of a fault code not listed, please get in touch!

1	Oxygen Sensor "A" (Primary)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	ECU will probably not run in closed loop operation.
Comment	With OBD-0 VTEC ECU's such as the PW0 and PR3 that run two primary oxygen sensors (one for each pair of cylinders) make sure you have the correct sensor in the correct manifold boss!

2	Oxygen Sensor "B"
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	More details to follow. Secondary oxygen sensor's purpose is typically to monitor the performance of the catalytic converter.

3	MAP Sensor (Manifold absolute pressure)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	To follow, please see details for fault code 5.

4	CKP Sensor (Crankshaft position)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	To follow.

5	MAP Sensor (Manifold absolute pressure)
Honda say	Defective circuit or unplugged / defective sensor / incorrect pipework.
Implications	ECU will run TPS based routine.
Comment	The MAP sensor is the primary load input, and on failure the ECU will run some form of substitution based on the TPS input. Engine will run, although generally not idle and performance is severely impaired. Do not run the engine any longer than required to get the car to a repair shop.

6	ECT Sensor (Engine coolant temperature)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	ECU will ignore the input if it is not within range, and substitute a fixed value.
Comment	Fixed value substituted when input is not in range varies depending on engine RPM - commonly 85°C during normal operation, although this is raised during cranking.

7	TP Sensor (Throttle position)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	Incorrect adjustment or failure of the TPS sensor or wiring issues will cause a number of problems, mainly idle related. Details of adjustment procedure to follow.

8	TDC Sensor (Top dead centre)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	To follow.

9	CYP Sensor (Cylinder position)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	To follow.

10	IAT Sensor (Intake air temperature)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	ECU will ignore the input if it is not within range, and substitute a fixed value.
Comment	Details of fixed value used to follow.

11	IMA Sensor (Idle mixture adjust)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	Probably substitution of fixed value if input is not within range.
Comment	Sometimes known as the CO Pot. This is fitted to OBD-0 ECU's in some vehicles that do run an lambda sensor. This only applies to some some markets, like the UK where fitting of a catalytic converter was not law until 1991. The input is simply a potentiometer that is used to trim the base fuelling - hence the name CO pot.

12	EGR Lift Sensor (Exhaust gas recirculation)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	Unknown.
Comment	EGR is used for emission control.

13	BARO Pressure Sensor (Atmospheric pressure sensor)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	ECU will ignore the input if it is not within range, and substitute a fixed value.
Comment	This sensor is commonly fitted with US and European ECU's, it is not normally found on JDM units. With OBD-0 ECU's this sensor is external to the ECU and on all later units (including OBD-0 VTEC ecu's such as the PW0) it is a small module fitted internally to the PCB.

14	IAC Valve (Idle Air Control)
Honda say	Defective circuit or unplugged / defective valve.
Implications	Unknown.
Comment	Only applies to vehicles equipped with an automatic transmission.

15	Ignition Output Signal
Honda say	Missing or defective ignition output signal.
Implications	To follow.
Comment	To follow.

16	Fuel Injector System
Honda say	Defective circuit or unplugged / defective sensor.
Implications	Unknown.
Comment	Problem with fuel injectors.

17	VSS (Vehicle Speed Sensor)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	If engine is VTEC model, it will not be engaged.
Comment	Early 1990 VSS sensors as fitted to B series engined MK2 Integra's and MK2 CRX's are prone to failure - the design was modified and late 1991-onwards vehicles rarely get VSS problems.

18	Ignition Timing
Honda say	Unknown.
Implications	Unknown.
Comment	Not quite sure about this one!

19	Automatic Transmission Lock Up Control Solenoid Valve
Honda say	Defective circuit or unplugged / defective solenoid valve .
Implications	Unknown.
Comment	Only applies to vehicles equipped with an automatic transmission.

20	ELD (Electrical Load Detector)
Honda say	Defective circuit or unplugged / defective solenoid valve .
Implications	Unknown.
Comment	This is a solid-state hall effect current sensor, commonly mounted in the engine compartment's fuse box (normally located on top of a suspension turret) and it's purpose is to monitor current demand for precise emission control.

21	VTEC Solenoid Valve
Honda say	Defective circuit or unplugged / defective solenoid valve.
Implications	VTEC will not be engaged, no high cam lobes.
Comment	Solenoid, or "spool" valve that allows oil to flow into the VTEC mechanism. VTEC will obviously not operate and engine will feel breathless at higher RPM's. High RPM driving should be avoided as the engine will only be operating on the low speed lobes.

22	VTEC Oil Pressure Switch
Honda say	Defective circuit or unplugged / defective pressure switch.
Implications	VTEC will not be engaged, no high cam lobes.
Comment	This switch was only used on early VTEC engines - note it is not to be confused with the oil pressure switch. Commonly caused by idiots who don't check their oil level - so if it flashes up during hard cornering or braking then stop and immediately and check the dipstick! The VTEC mechanism is operated hydraulically from the engine's main oil supply and when it is first engaged causes a momentary fluctuation in oil pressure, and demand on the pump - if pressure available to the VTEC mechanism is not high enough, it will disable VTEC.

23	KS (Knock Sensor)
Honda say	Defective circuit or unplugged / defective pressure sensor.
Implications	To follow.
Comment	ECU will be unable to trim ignition timing to adapt for differing environmental conditions, and quality of fuel.

30	Automatic Transmission Signal "A" SEAF / SEFA / TMA or TMB
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	To follow.

31	Automatic Transmission Signal "B"
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	To follow.

41	Primary Oxygen Sensor - Heater
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	To follow.

43	Fuel Supply System - Oxygen Sensor (A)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	This is generally flagged when the engine is running either very rich, or lean due to a mechanical problem, or very bad tuning. Based on Lambda sensor input to some extent. Get a wideband AFR meter on the car - also check your injectors and fuel pressure.

44	Fuel Supply System - Oxygen Sensor B
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	See fault code 43. Only a small number of Honda vehicles use a "B" O2 sensor such as the first generation B16A engines (PW0 ECU) and some V6 models. Each O2 sensor is responsible for a group of cylinders and during closed loop operation fuel delivery to each group of cylinders is trimmed independently. Because of this it is absolutely imperative that you have each O2 sensor in it's respective manifold port. If you mix up the sensor locations or wiring the ECU will alter the fuel delivery for the wrong cylinder bank. This can result in hesitation and misfires during light to moderate loads.

48	LAF Sensor (Lean Air Fuel)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	To follow.

54	CKF Sensor (Crankshaft Speed Fluctuation)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	This sensor is mounted behind the timing belt sprocket on the crank, and used to closely monitor the speed of the crank to detect a misfire etc. Only fitted to OBD-2 systems.

58	TDC Sensor 2 (Top Dead Centre)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	To follow.

61	Oxygen Sensor, Heated - Sensor 1 (Primary)
Honda say	High voltage, low voltage or slow response.
Implications	To follow.
Comment	To follow.

63	Oxygen Sensor, Heated - Sensor 2 (Secondary)
Honda say	High voltage, low voltage or slow response.
Implications	To follow.
Comment	To follow.

65	Oxygen Sensor Heater (Secondary)
Honda say	Defective circuit or unplugged / defective sensor.
Implications	To follow.
Comment	To follow.

67	Catalyst System Efficiency Below Threshold
Honda say	Malfunctioning or defective catalyst system.
Implications	To follow.
Comment	To follow.

70	Automatic Transmission
Honda say	Malfunction with the automatic transmission controls.
Implications	To follow.
Comment	To follow.

71	Cylinder 1 Missfire or a Random Missfire
Honda say	A condition is present that is creating a cylinder misfire.
Implications	To follow.
Comment	To follow.

72	Cylinder 2 Missfire or a Random Missfire
Honda say	A condition is present that is creating a cylinder misfire.
Implications	To follow.
Comment	To follow.

73	Cylinder 3 Missfire or a Random Missfire
Honda say	A condition is present that is creating a cylinder misfire.
Implications	To follow.
Comment	To follow.

74	Cylinder 4 Missfire or a Random Missfire
Honda say	A condition is present that is creating a cylinder misfire.
Implications	To follow.
Comment	To follow.

75	Cylinder 5 Missfire or a Random Missfire
Honda say	A condition is present that is creating a cylinder misfire.
Implications	To follow.
Comment	To follow.

76	Cylinder 6 Missfire or a Random Missfire
Honda say	A condition is present that is creating a cylinder misfire.
Implications	To follow.
Comment	To follow.

80	Exhaust Gas Recirculation
Honda say	Insufficient flow detected.
Implications	To follow.
Comment	To follow.

86	ECT Sensor (Engine Coolant Temperature)
Honda say	Insufficient flow detected.
Implications	To follow.
Comment	To follow.

90	Evaporative Emission Control System
Honda say	Leak detected in the fuel tank area.
Implications	To follow.
Comment	To follow.

91	Fuel Tank Pressure Sensor
Honda say	Low input.
Implications	To follow.
Comment	To follow.

92	Evaporative Emission Control System
Honda say	Insufficient purge flow.
Implications	To follow.
Comment	To follow.

Fault Code Descriptions

Fault Codes Explained