ECU CODES
Self Diagnostic indicator light
Symptom, Component or system area
Possible problem area
no blinks
Will not start
Check engine light stays on
Check the ECU fuses in the under hood & dash fuse boxes
Check ground at thermostat housing
Possible bad ECU
no blinks
Will not start
No check engine light reported on
Check ignition system (for spark, including distributor rotor)
Check compression (for possible soft carbon and also beware of broken
timing belts or seized cams )
Check ground wire to thermostat housing (No spark?)
Check for fuel pressure, injector pulse, or water in fuel
Check for water damaged ECU
Check main relay for PGM-FI system
Check power & ground to the ECU, possible bad ECU
1 blink
Oxygen sensor circuit (O2 "A" )
May fail emission test if code sets in that run cycle (bank 2 on V-6
models)
Short or open in O2 sensor circuit or bad O2 sensor
low fuel pressure, cylinder misfiring, fuel contamination or silicone
contamination, possible leaking head gasket
Injector problem or needs orifice in purge line (early models)
2 blinks
Oxygen sensor circuit (O2 "B")
Same as above (bank 1 on V-6 models)
3 blinks
Manifold Absolute Pressure (MAP)
Plugs usually wet, engine may stall or not rev
usually an electrical problem in the MAP sensor circuit
5 blinks
Manifold Absolute Pressure (MAP)
Plugs usually wet, engine may stall or not rev
usually an mechanical or hose problem with the MAP sensor circuit
4 blinks
Crank Angle Sensor circuit (CKP)
Engine does not rev, may idle erratic
Short or open in CKP circuit or bad CKP
Check T-belt position on DOHC models
6 blinks
Coolant Temperature Sensor circuit (TW or ECT) Engine idles high &
or hard to start when hot (usually)
Short or open in TW sensor circuit or bad TW Sensor
Also Coolant must be full for proper sensor operation
May also set code in A/T ECU
7 blinks
Throttle Angle Sensor circuit (TP)
Hesitation on acceleration, high idle speeds, engine may not rev when
cold
Short or open in TP sensor circuit or bad TP sensor
May also set code in A/T ECU
8 blinks
TDC Position Sensor circuit
Engine may not start, runs rough
Short or open in TDC sensor circuit or bad TDC sensor
Check T-belt position on DOHC models
9 blinks
#1 Cylinder Position Sensor circuit (CYL
or CYP) Engine may not start, runs rough
Short or open in CYL sensor circuit or bad CYL sensor
Check T-belt position on DOHC models
10 short blinks or 1 long blink
Intake Air Temperature circuit (TA or IAT)
Short or open in TA sensor circuit or bad TA sensor
12 short blinks or 1 long blink + 2 short blinks
Exhaust Gas Recirculation circuit (EGR)
Rough running or idling, Stalling
Short or open in EGR system wiring or broken hoses, plugged orifice
in air chamber, check EGR valve first
13 short blinks or 1 long blink + 3 short blinks
Atmospheric Pressure Sensor circuit (PA or BARO) Engine stalls, Hard
to start cold
Short or open in PA sensor wiring, bad PA sensor
14 short blinks or 1 long blink + 4 short blinks
Electronic Air Control circuit (EACV or IAC Valve) High idle, Low
idle, Stalling
Short or open in EACV wiring, bad EACV valve
Low idle? no code-check Idle Adjustment port for plugging
*15 short blinks or 1 long blink + 5 short blinks
Ignition Output Signal Failure
Engine may not start
Short or open in ignition circuit causing no spark or no RPM imput
to the ECU, Bad ignitor, coil, or distributor assembly
*16 short blinks or 1 long blink + 6 short blinks
Fuel Injector circuit
Engine may not start, misfires, loss of power or fails emission test
Short or open in fuel injector wiring, bad fuel injector, bad main
relay
*Note that early models did not have the luxury of this code
17 short blinks or 1 long blink + 7 short blinks
Vehicle Speed Sensor (VSS)
Cruise control may not operate
Short or open in VSS wiring, check for bad VSS first
May also set code on A/T ECU, A/T lockup inoperative
19 short blinks or 1 long blink
+ 9 short blinks
A/T lock solenoid (equipped Civics only)
A/T lock-up fails to operate
Short or open in lock up wiring, a contaminated lock up solenoid,
problem in the transmission will not cause this
20 short blinks or 2 long blnks
Electronic Load Detector (ELD)
Short or open in ELD wiring, bad ELD, check charging sys
21 = 2 long blinks + 1 short
VTEC Solenoid valve (VTEC car only)
Short or open in VTEC wiring, Bad VTEC solenoid valve
22 = 2 long blinks + 1 short
VTEC oil pressure switch (VTEC car only)
Short or open in VTEC wiring, Bad VTEC o.p.s.(V-6 bank 2)
23 = 2 long blinks + 1 short
L. Knock sensor (Bank 2)
Short or open in knock sensor wiring, bad knock snsr, PCM
30 = 3 long blinks
A/T control signal A No symptom
Short or open wiring between ECU & AT ECU or bad ECU
31 = 3 long blinks + 1 short blink
A/T control signal B
No symptom
Short or open in wiring between ECU & AT control unit or bad ECU
35 = 3 long blinks + 5 short
TCS line failure (TCS may not function)
Problem in Traction control system or wiring
36 = 3 long blinks + 6 short
TCS low or High imput
same as above
37 = 3 long blinks + 7 short blinks
Accelerator position sensor
Short or open in accelerator position sensor circuit or bad
accelerator position sensor or ECU
40 = 4 long blinks
Throttle position abnormal
Problem in Throttle valve control motor circuit, or motor
41 = 4 long blinks + 1 short blink
Oxygen sensor heater circuit (HO2S)
Fails Emission test
Short or open in HO2S wiring, bad HO2S
(Bank 2 sensor 1 on V-6)
42 = 4 long blinks + 2 short
Right primary HO2S (V-6 models)
Short or open in HO2S wiring, bad HO2S (V-6 bank 1 sensor 1)
43 = 4 long blinks + 3 short blinks
Oxygen sensor circuit (O2) or fuel supply system Fails emission test
Short or open in O2 sensor circuit, bad O2 sensor, fuel supply
problem or fuel contamination
45 = 4 long blinks + 5 short blinks
Running too lean or rich ( bank 2 on V-6 models)
Fuel system problem or contamination, primary HO2S or possible MAP
sensor malfunction, valves
46 = 4 long blinks + 6 short blinks
Running too rich or lean (bank 1 on V-6 models)
Same as code #45
48 = 4 long blinks + 8 short
LAF Sensor circuit
Short or open in LAF sensor circuit, bad LAF sensor
52 = 5 long blinks + 2 short blinks
VTEC system (bank 1 on V6)
Short or open in rear VTEC solenoid or Pressure switch wiring, bad
solenoid valve or pressure switch or ECU
53 = 5 long blinks + 3 short blinks
R. Knock sensor (bank 1on V6)
Short or open in knock sensor wiring, bad knock sensor, PCM
54 = 5 long blinks + 4 short
CKF Sensor 2 (crank speed variance)(V6)
Timing belt jumped teeth, bad CKF sensor or wiring, PCM
58 = 5 long blinks + 8 short
TDC sensor 2 (runs rough)(V6)
Short or open in TDC sensor wiring, bad TDC sensor
59 = 5 long blinks + 9 short
Cylinder Position sensor 2 (runs rough)V6
Short or open in the sensor wiring or bad sensor
61 = 6 long blinks + 1 short
L. Primary HO2S (slow reaction) bank 2
Bad L. primary HO2S, check exhaust pipe (sensor 1)
62 = 6 long blinks + 2 short
R. Primary HO2S (slow reaction) bank 1
Bad R. primary HO2S, check exhaust pipe (sensor 1)
63 = 6 long blinks + 3 short blinks
Secondary HO2S (reads high, low, slow)
Short or open in secondary HO2S wiring, or bad sensor.
or ECU (Bank 2 sensor 2 on V-6 models)
64 = 6 long blinks + 4 short
Secondary HO2S (reads high, low, slow)
same as code# 63. Bank 1 sensor 2 (V-6 )
65 = 6 long blinks + 5 short
Secondary HO2S heater circuit
Short or open in secondary HO2S heater wiring, bad sensor
or ECU (bank 2 sensor 2 on V-6 models)
66 = 6 long blinks + 6 short
Secondary HO2S heater circuit
same as code # 65 (bank 1 sensor 2 on V-6)
67 = 6 long blinks + 7 short
Catalyst system below threshold
Bad catalyst
70 = 7 long blinks
Electronic automatic transmission control
Problem in EAT control circuits
71 = 7 long blinks + 1 short
Cylinder #1 misfire or random misfire
Lack of power, hesitation
Problem in ignition system, fuel injector, MAP sensor, EGR system,
Contaminated fuel, Low compression, out of fuel
72 = 7 long blinks + 2 short
Cylinder #2
same as code # 71
73 = 7 long blinks + 3 short
Cylinder #3
same as code # 71
74 = 7 long blinks + 4 short
Cylinder #4
same as code # 71
75 = 7 long blinks + 5 short
Cylinder #5 (V-6)
same as code # 71
76 = 7 long blinks + 6 short
Cylinder #6 (V-6)
same as code # 71
79 = 7 long blinks + 9 short
Spark plug voltage detection circuit
Short or open in circuit, bad spark plug detection module
80 = 8 long blinks
EGR low flow (light surge @ cruise)
EGR valve or restricted EGR port
86 = 8 long blinks + 6 short
Coolant temperature sensor (TW or ECT)
Bad ECT sensor, check cooling system (out of range)
90 = 9 long blinks
Evaporative emissions control system
Leak detected in fuel tank, check gas cap
91 = 9 long blinks + 1 short
Fuel tank pressure sensor
Low pressure, check gas cap
92 = 9 long blinks + 2 short
Evaporative system purge flow incorrect
EVAP purge flow solenoid valve, Purge flow switch, or circuits,
check tubing & purge port, PCM