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

NOTE: Code 12 is used during diagnostic test procedure to check the diagnostic and code display ability of the ECM. This code indicates that ECM is not receiving DIS reference signal. Signal occurs with ignition switch in "ON" position and the engine not running.

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.

Safety Warning

Est Performance Check

Use the Manual With the Right Hardware

When to See a Mechanic

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