Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSPONTIAC1991FIREBIRD FORMULA, 5.0 F, STANDARD, M39REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 10 (ENGINE CONTROLS - TESTS W/CODES - 3.3L PFI)
1991 Pontiac Firebird Formula, 5.0 F, Standard, M39
Section 10 (Engine Controls - Tests W/Codes - 3.3L PFI)
1991 Pontiac Firebird Formula, 5.0 F, Standard, M39SECTION Section 10 (Engine Controls - Tests W/Codes - 3.3L PFI)
WARNING: This page is about a different car, the 1991 Oldsmobile Cutlass Cruiser, 1991 Oldsmobile Cutlass Ciera, 1991 Oldsmobile Cutlass Calais, 1991 Buick Skylark, and 1991 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
- Introduction
- Self-Diagnostic System
- Notes
- Hard Failures
- Intermittent Failures
- Diagnostic Procedure
- Retrieving Codes (Non-Scan)
- Reading Trouble Codes
- Trouble Code Definition
- Hard Or Intermittent Trouble Code Determination
- Clearing Trouble Codes
- ECM/Pcm Location
- Diagnostic Materials
- Special Tools (Diagnostic)
- Scan Tester Usage
- Scan Data
- Test Procedure Summary
- Diagnostic Flow Charts For Codes: 13 To 66
- Notes
- Code 13, Open Oxygen Sensor Circuit
- Code 14, Coolant Temperature Sensor Signal Voltage Low
- Code 15, Coolant Temperature Sensor Signal Voltage High
- Code 16, System Voltage High
- Code 21, Throttle Position Sensor Signal Voltage High
- Code 22, Throttle Position Sensor Signal Voltage Low
- Code 24, Vehicle Speed Sensor (VSS)
- Code 26, (1 Of 3) Quad-Driver Circuit
- Code 26, With 3T40 Trans. Quad-Driver Circuit (2 Of 3)
- Code 26, (3 Of 3), Quad-Driver Circuit
- Code 27 Or 28, With 3T40 Transaxle Gear Switch Circuits
- Code 28 Or 29, A Body With 4T60 Trans, Gear Switch Circuits
- Code 31, Park/Neutral Switch Circuit
- Code 33, Map Sensor Signal Voltage High
- Code 34, Map Sensor Signal Voltage Low
- Code 34, MAF Sensor Signal Voltage Low
- Code 35, IAC Idle Speed Error
- Code 35, IAC Idle Speed Error Using Tech I
- Code 38, Brake Switch Circuit
- Code 39, With 3T40 Transaxle, TCC Circuit
- Code 39, With 3T40 Trans. TCC Circuit Using Tech 1
- Code 39, With 4T60 (440-T4) Trans. TCC Circuit
- Code 39, With 4T60, TCC Circuit Using Tech 1
- Code 42, Est Circuit Open Or Grounded
- Code 43, ESC Error Without ESC Module
- Code 44, Lean Exhaust Indication
- Code 45, Rich Exhaust Indication
- Code 46, Power Steering Pressure Switch
- Code 48, Misfire Diagnosis
- Code 51, Faulty Prom/Mem-Cal
- Code 52, Faulty CALPAK
- Code EO51, Faulty Prom/Mem-Cal
- Code 66, N Body, A/C Pressure Sensor
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.