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Eric, Automotive Repair Shop Manager
Category: Buick
Satisfied Customers: 29721
Experience:  20+ yrs. experience as repair shop manager and technician.
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1990 Buick Century: V6..Service engine soon light turns

Resolved Question:

1990 Buick Century 3.3 V6. Service engine soon light turns on & off frequently. Low idle speed, engine stumbles & sometimes dies at stop sign but has good power when accelerating. Replaced idle air control valve & vacuum line between vacuum block and fuel regulator. Could it be a bad fuel regulator? Please help, very frustrated. Don't have the money to pay to have someone fix it.

Submitted: 7 years ago.
Category: Buick
Expert:  Eric replied 7 years ago.



Have you pulled the fault codes yet? If not, do you know how to do this yourself?

Customer: replied 7 years ago.
No & no
Expert:  Eric replied 7 years ago.



Ok, we need to do that first before throwing any more parts at. Accurate diagnositics is critical in repairing the problem and not costing you a fortune in replacing parts that are actually good.


Diagnostic Trouble Codes - 1990

13 Open Oxygen Sensor Circuit
14 Coolant Temperature Sensor (High Temp Indicated)
15 Coolant Temperature Sensor (Low Temp Indicated)
16 System Voltage High
21 Throttle Position Sensor (Signal Voltage High)
22 Throttle Position Sensor (Signal Voltage Low)
23 Manifold Air Temperature (MAT) Circuit (Low Sig.)
24 Vehicle Speed Sensor (VSS) Circuit
25 Manifold Air Temperature (MAT) High Temp Indicated
26 Quad-Driver (QDM) Circuit
Gear Switch Diagnosis
Gear Switch Diagnosis
31 Park/Neutral Switch Circuit
34 Mass Air Flow Sensor (MAF) (GM/SEC Low)
38 Brake Input Circuit
39 Torque Converter Clutch (TCC) Circuit
42 Electronic Spark Timing (EST) Circuit
43 Electronic Spark Control (ESC) Circuit
44 Oxygen Sensor Circuit (Lean Exhaust Indicated)
45 Oxygen Sensor Circuit (Rich Exhaust Indicated)
46 Power Steering Pressure Switch (PSPS) Circuit
48 Misfire Diagnosis
51 Mem-Cal Error
66 Low A/C Refrigerant Charge
69 A/C Head Pressure Switch Circuit

To extract a trouble from the computer for diagnostic purposes, the Assembly Line Communication Link (ALDL) connector is used.

Ground terminals A and B with the ignition "ON" and engine not running. The system will enter the diagnostic mode. In this mode, the computer will display a 12, three consecutive times, by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" or light. A 12 consists of one flash, a short pause, then two flashes in rapid succession.

After 12 is displayed, any stored trouble s will be displayed by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" light. All s are displayed 3 times each then a 12 will repeat. In the diagnostic mode, the computer will also energize all computer controlled relays and solenoids.

ALDL Connector (Located Front seating area, driver side, under dash, mounted near fuse panel )


Once you retreive the codes, if you have a question on either diagnosing the code or replacing a part, just re-open this question and I will continue to help



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