Foxbody Mustang EEC-IV Error Codes

If there is an issue with your Foxbody Mustang (engine related), a good place to start is to check if the EEC-IV computer has registered any error codes. There are two ways to do so:

  1. Code scanner: You can buy a code scanner from almost any auto parts store, just verify that it can indeed read the error codes from Foxbody Mustangs. Plugin the code scanner to VIP/DLC connector harness in the engine bay (right-hand, driver side for 86-93) and read out any error codes, if there are any.
  2. Test light: For the procedure on how to pull the error codes from a Foxbody Mustang EEc-IV equipped car, please refer to: DIY KOEO/KOER/Cylinder Balance Self-Test Procedure
Listed below are the possible error codes thrown by the Mustang EEC-IV computer. Accompanied with each code is the potential reason why an error has occured.


Legend: O = Ignition On (accessory), R = Engine Running, C = Continuous Memory
Code Test Condition Cause
11 O,R,C System OK, testing complete
12 R Idle speed control out of specified range
13 O,R,C Normal idle not within specified range
14 O,C Ignition profile pickup erratic
15 O ROM test failure
15 C Power interrupt to computer memory
16 R Erratic idle, oxygen sensor out of range or throttle not closing
17 R Curb idle out of specified range
18 R SPOUT circuit open
19 O No power to processor
19 R Erratic idle speed or signal
21 O,R Coolant temperature out of specified range
21 O,R,C Coolant temperature sensor out of specified range
22 O,R,C MAP sensor out of specified range
23 O,R,C Throttle position signal out of specified range
24 O,R Air charge temperature low
25 O,R Mass Air Flow sensor or circuit
27 C Vehicle Speed Sensor or circuit
28 0,R Vane air temperature sensor or circuit
29 C No continuity In Vehicle Speed Sensor circuit
31 O,R,C Canister or EGR valve control system
32 O,R,C Canister or EGR valve control system
33 R,C Canister or EGR valve not operating properly
34 O,R,C EVP voltage above closed unit
35 O,R,C EGR pressure feedback, regulator circuit
38 C Idle control circuit
39 C Automatic overdrive circuit
41 C Oxygen sensor signal
41 R Lean fuel mixture
42 R,C Fuel mixture rich
43 C Lean fuel mixture at wide open throttle -
43 R Engine too warm for test
44 R Air management system inoperative
45 R Thermactor air diverler circuit
46 R Thermactor air bypass circuit
47 R Low flow of unmetered air at idle
48 R High flow of unmetered air at idle
49 C SPOUT signal defaulted to 1 0-degrees
51 O,C Coolant temperature sensor out of specified range
52 O,R Power steering pressure switch out of specified range
53 O,C Throttle Position Sensor input out of specified range
54 O,C Vane air flow sensor or air charge temperature sensor
55 R Charging system under specified voltage (1984 through 1988)
55 R Open ignition key power circuit (1984 through 1988)
56 O,R,C Mass Air Flow sensor or circuit
57 C Transmission neutral pressure switch circuit
58 O CFI - idle control circuit; EFI - vane air flow circuit
58 R Idle speed control motor or circuit
58 C Vane air temperature sensor or circuit
59 O,C Transmission throttle pressure switch circuit
61 O,C Coolant temperature switch out of specified range
62 0 Transmission circuit fault
63 O,C Throttle Position Sensor or circuit
64 O,C Air Charge Temperature (ACT) sensor
65 C Fuel control system not switching to closed loop
66 O,C No Mass Air Flow sensor signal
67 O,R,C Neutral drive switch or circuit
67 C Air conditioner clutch switch circuit
69 O,C Vehicle Speed Sensor or circuit
72 C System power circuit, electrical interference
72 R No Manifold Absolute Pressure or Mass Air Flow sensor signal fluctuation
73 O,R Throttle Position Sensor or circuit 21
74 R Brake on/off ground circuit fault 21
75 R Brake on/off power circuit fault 22
76 R No vane airflow change
77 R Throttle "goose" test not performed
78 C Power circuit 1
79 O Air conditioner clutch circuit
81 O Thermactor air circuit
82 O Thermactor air circuit, integrated controller circuit
83 O EGR control circuit (four-cylinder models oeM
83 O Cooling fan circuit (V6 models only)
83 O,C Low speed fuel pump relay (1984 through 1988 models)
83 O,C EGR solenoid or circuit (1989 and later models)
84 O,R EGR control circuit
85 O,R Canister purge circuit or transmission shift control circuit
85 C Excessive fuel pressure or flow
85 C Canister purge circuit
86 C Low fuel pressure or flow
87 O,R,C Fuel pump circuit D2
88 O Integrated controller
89 O Lock-up solenoid
91 R,C Oxygen sensor problem, fuel pressure out of specified range or injectors out of balance
92 R Fuel mixture rich, fuel pressure high
93 O Throttle Position Sensor or circuit D
94 R Secondary air system inoperative
95 O,C Fuel pump circuit problem
95 R Thermactor air diverter circuit
96 O,C Fuel pump circuit
96 R Thermactor air bypass circuit
98 R Repeat test sequence
99 R Repeat test sequence
99 R System has not learned to control idle speed
111 O,R,C System Pass
112 O,R,C Air Charge Temp (Ad) Sensor circuit below minimum voLtagE/ 254 F
113 O,C Air Charge Temp (ACT) Sensor circuit above maximum voltagE/ -40 F
114 O,R Air Charge Temp (ACT) out of self test range
116 O,R Coolant Temp (ECT) out of self test range
117 O,R Coolant Temp (EdT) Sensor circuit below minimum voltage/ 254 F
118 O,C Coolant Temp (EdT) Sensor circuit above maximum voitage/ -40 F
121 O,C Closed Throttle Voitage higher or lower than expected
122 O,R,C Throttle Position (TP) Sensor circuit below minimum voltage
123 O,C Throttle Position (TP) Sensor circuit above maximum voltage
124 O,C Throttle Position (TP) Sensor voltage higher than expected
125 C Throttle Position fTP) Sensor voltage lower than expected
126 C BP Sensor higher or lower than expected
129 O,R,C Insufficient Mass Air Flow (MAE) change during Dynamic Response Test
144 C No Oxygen Sensor (HEGO) Switches detected
157 C Mass Air Flow (MAE) Sensor circuit below minimum voltage
158 O,C Mass Air Flow (MAE) Sensor circuit above maximum voltage
159 O,R Mass Air Flow (MAE) Sensor out of self test range
167 R Insufficient Throttle Position change during Dynamic Response Test
171 C Fuel system at adaptive limits, Oxygen Sensor (HEGO) unable to switch
172 R,C Lack of Oxygen Sensor (HEGO) Switches, indicates lean
173 R,C Lack of Oxygen Sensor (HEGO) Switches, indicates rich
179 C Fuel system at lean adaptive limit at part throttle, system rich
181 C Fuel system at rich adaptive limit at part throttle, system lean
182 C Fuel system at lean adaptive limit at idle, system rich
183 C Fuel system at flch adaptive limit at idle, system lean
184 C Mass Air Flow (MAE) higher than expectec
185 C Mass Air Flow (MAE) lower than expected
186 C Injector pulse width higher than expected
187 C Injector pulse width lower than expected
211 C Profile Ignition Pickup (PIP) circuit fault
212 C Ignition module circuit failure - SPOUT circuit grounded
213 R SPOUT circuit
214 C Cylinder Identification (CID) circuit failure
215 C EEC Processor detected Coil 1 primary circuit failure
216 C EEC Processor detected Coil 2 primary circuit failure
218 C Loss of ignition Diagnostic Monitor (1DM) signal-left side
222 C Loss of Ignition Diagnostic Monitor (1DM) signal-right side
223 C Loss of Dual Plug Inhibit (DPI) control
224 C Erratic Ignition Diagnostic Monitor (1DM) input to processor
225 R Knock riot sensed during Dynamic Response Test
327 O,R,C EVP circuit below minimum voltage
328 O,R,C EGR "closed valve" voltage lower than expected
332 R,C Insufflcjent EGR flow detected
334 O,R,C EGR closed valve voltage higher than expected
337 O,R,C EVP circuit above maximum voltage
341 O Octane Adjust Service Pin in use
411 R Cannot control RPM during KOER low rpm check
412 R Cannot control rpm during KOER high rpm check
452 C Isufflcient input from Vehicle Speed Sensor (VSS)
511 O EEC Processor Read Only Memory (ROM) test failure
512 C EEC Processor Keep 4Jive Memory (KAM) test failure
519 O Power Steering Pressure Switch (PSPS) circuit open
521 R Power Steering Pressure Switch (PSPS) circuit did not change states
522 O Vehicle not in PARK or NEUTRAL during KOEO
528 C Clutch Switch Circuit failure
536 R,C Brake On/Off (BOO) circuit failure I not actuated during KOER
538 R IsuffIcient RPM change during KOER Dynamic Response Test
539 O AC On/Defrost ON during KOEO
542 O,C Fuel Pump secondary circuit failure
543 O,C Fuel Pump secondary circuit failure
556 O,C Fuel Pump Relay primary circuit failure
558 O EGR Vacuum Regulator (EVR) circuit failure
564 0 ElectrOD FAN( EDF) circuit failure
565 O Canister Purge (CANP) circuit failure
566 O 3-4 Shift Solenoid circuit failure
629 O Converter Clutch Control circuit failure
998 O,R Hard Fault present
Legend: O = Ignition On (accessory), R = Engine Running, C = Continuous Memory

A text and printable version of the EEC-IV code list is available here