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.
1990 Geo Tracker Base, StandardFACTORY OEM SERVICE PROCEDURE
Engine Controls - Tests W/Codes
- Introduction
- Self-Diagnostic System
- Diagnostic Flow Charts
- Diagnostic Circuit Check
- Chart A-1, No Check Engine Light
- Chart A-2, Won't Flash Code 12 Check Engine Light On Steadily
- Chart A-3, Engine Cranks But Will Not Run
- Chart A-5 - Fuel Injector & Circuit Check
- Chart A-7A, Fuel System Diagnosis
- Chart A-7B, Fuel System Diagnosis - Pressure Check
- Chart A-8, Control Relay Circuit Check
- Chart C-1, ECM Circuit Resistance Check
- Diagnostic Code Charts
- Code 13, Oxygen Sensor Circuit Open Circuit
- Code 14, Coolant Temperature Sensor (Cts) Circuit Low Temperature Indicated
- Code 15, Coolant Temperature Sensor (Cts) Circuit High Temperature Indicated
- Code 21, Throttle Position Sensor (TPS) Circuit Signal Voltage High
- Code 22, Throttle Position Sensor (TPS) Circuit Signal Voltage Low
- Code 23, Manifold Air Temperature (Mat) Sensor Circuit Low Temperature Indicated
- Code 25, Manifold Air Temperature (Mat) Sensor Circuit High Temperature Indicated
- Code 31, Manifold Absolute Pressure (Map) Sensor Circuit Signal Voltage High - Low Vacuum
- Code 32, Manifold Absolute Pressure (Map) Sensor Circuit Signal Voltage Low - High Vacuum
- Code 41, Ignition Signal Circuit No Signal
- Code 42, 5TH Gear Switch Circuit Grounded Circuit M/T Only)
- Code 42, Torque Converter Clutch Lock-Up Signal Circuit Signal Voltage Remains On At All Times (A/T Only)
- Code 44, Idle Switch Circuit Open Or MISADJUSTED
- Code 45, Idle Switch Circuit Circuit Grounded Or MISADJUSTED
- Code 51, EGR System & Exhaust Gas Recirculated Temperature EGRTS) Temperature Too Low Or Too High (CALIF. Only)
- Code 53, Ground Circuit Open (CALIF. Only)
- Summary
Factory Service Tools
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.