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.
Est Performance Check
The ECM will set timing at a specified value when diagnostic test terminal of ALDL connector is grounded. To check EST operation, perform the following steps:
1) Start and run engine at 1500 RPM with ALDL diagnostic test terminal NOT grounded, and then with terminal grounded. If EST is operating properly, there should be a noticeable change in engine RPM. A fault in the EST system will set Code 41.
2) If Code 42 is set, use appropriate chart for diagnosis. If symptom is an engine miss and the direct ignition system is suspected, use CHART C-4D DIS MISFIRE for proper diagnosis. See the appropriate TESTS W/ CODES article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE sections under the ENGINE PERFORMANCE category. Refer to the following menu:
- 2.0L, VIN 1, see: 2.0L VIN [1] TBI TESTS W/CODES
- 2.5L, VIN U, see: 2.0L VIN [K] / 2.5L VINS [R & U] TESTS W/CODES
- 2.8L, VINS S, W & 9 see: 2.8L PFI TESTS W/CODES
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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.