Fault reader

[Choosing a name is hard]

On a 1985 c4 is the plug for fault reading different from an obd2 reader ?

 

[teamzr1]

1984-85 C4s are weird birds
They did not even function as OBD-I so there is no code reader or scanner for them
You need to do is the 12 pin diag connector under the dash

Jump terminals A and B on the ALDL

You view the connector pins, you will find the top row fully populated, whereas not all are populated pin on the bottom row.
On the top row (as you view the connector from the cockpit), the pin designators are F,E,D,C,B,A.

Here is a typical 12 pin connector.


(Some have more pins on the lower row than this example).
The pins you are interested in are those two pins in the top, right-hand portion of the connector, designated pins "A" and "B". Pin "B" is the diagnostic enable pin and pin "A" is ground.
By grounding pin "B", you enable the diagnostic readout functionality of the ECM/PCM.
Turn the key on, but don't start the car.

Watch the Check Engine Light flash.

You should get 3 "12" codes at the beginning, then any stored Diagnostic Trouble Codes, then 3 "12" codes at the end.

A "12" code would be as follows:
Flash, pause, flash flash....followed by a long pause.
That will repeat 3 times. Then for example, if you had a "34" code stored, it would be: flash flash flash (3), pause, flash flash flash flash. (4)

DTC Codes : may be different for model C4 years

C4 ECM Error Codes
DTC	Circuit or Sensor
11	Malfunction Idicator Lamp Circuit - VIN P Only
13	Oxygen Sensor Circuit
14	Coolant Sensor Circuit (High)
15	Coolant Sensor Circuit (Low)
16	Ignition Pblms (Used on 1992-1996 models only)
18	Injector Circuits - VIN P
21	Throttle Position Sensor (TPS) (High)
22	Throttle Position Sensor (TPS) (Low)
23	Intake Air Temperature (Low)
24	Vehicle Speed Sensor (VSS)
25	Intake Air Temperature (High)
26	Quad Driver Module Number 1 - VIN P
27	Quad Driver Module Number 2 - VIN P
28	Quad Driver Module Number 3 - VIN P
29	Secondary Air Injection Pump Circuit - VIN P
31	Camshaft Position Sensor - VIN J Only
32	Exhaust Gas Recirculation Circuit
33	Mass Air Flow Sensor Circuit (1985-1990)
33	Manifold Absolute Pressure High (1984 and LT-5)
34	Mass Air Flow Circuit (1985-1990)
34	Manifold Absolute Pressure Low (1984 and LT-5)
35	Idle Air Control Circuit (IAC) - VIN P
35	Manifold Absolute Pressure (MAP) - VIN J
36	Mass Air Flow Burn Off Circuit - VIN P
36	Electronic Ignition System Missing or Extra IC Signal - VIN J
37	Brake Switch Stuck On - VIN P
38	Brake Switch Stuck Off - VIN P
41	Cylinder Select Error Circuit (1985-1991 and LT-5) bad E-Prom
41	Ignition Control (IC) Circuit Open (1994-96)
42	Electronic Spark Timing Circuit (EST) IC Shorted - VIN P
42	Ignition Control (IC) Timing Circuit - VIN J
43	Knock Sensor Circuit
44	Bank 1 (Left Front) O2 Lean Exhaust Indicated
45	Bank 1 O2 Rich Exhaust Indicated
46	VATS Anti Theft Circuit Fault - VIN P
47	Knock Sensor Circuit or Module Missing - VIN P
48	Mass AirFlow (MAF) Sensor - VIN P
50	System Charging Voltage Low - VIN P
51	PROM/EEPROM Error
52	Oil Temperature Circuit (Low Temperature)
53	System Charging Voltage High
54	Fuel Pump Circuit (Low Voltage)
55	Engine Fuel Running Lean
56	Secondary Air Inlet Valve Actuator Vaccum - VIN J
58	Trannie Fluid Temp Circuit low
59	Trannie Fluid Temp Circuit High
61	Secondary Air Inlet Valve Actuator Valve - VIN J
62	Engine Oil Temperature Circuit (High Temperature)
63	Bank 2 Oxygen Sensor Circuit (Open)
64	Bank 2 Oxygen Sensor Circuit (Lean Exhaust)
65	Oxygen Sensor Circuit (Rich Exhaust)
66	Air Conditioner Pressure Open or Shorted
66	Valet Power Switch - VIN J
67	Air Conditioner Pressure Limit Exceeded
68	Air Conditioner Relay Fault
69	Air Conditioner Clutch Fault
70	A/C Clutch Relay Driver
72	Speed Sensor Loss or Gear Selector Switch Fault (Start Lockout)
73	Pressure Control Solenoid - PCM only Circuit
74	Traction Control System - Low
75	Trannie System Voltage Low
77	Primary Cooling Fan Relay Control
78	Secondary Cooling Fan Relay Control
79	Trannie Fluid OverTemp
80	Trannie Component Slipping
81	Trannie 2-3 Shift Solenoid
82	Trannie 1-2 Shift Solenoid
84	3-2 Control Solenoid - Auto Trannie
84	2-3 Gear Blockout Relay - Manual Trannie
85	Trannie TCC Stuck On
90	Trannie TCC Solenoid
91	1 to 4 Upshift Lamp - Manual
97	VSS Output Circuit (Speedo)

 

[Choosing a name is hard]

As always thank you .i thought the plug looked odd willl try this next week when my buddy is over as this car is a joint venture

 

[Steven Smith]

As Teamzr1 said the method above is the easiest way to read codes but if you want to get a bit more technical have a look here.

OBD Diagnostics

aldlcable.com