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 MANUALSGEO1993PRIZM L4-1600CC 1.6L DOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTESTING AND INSPECTIONSCAN TOOL TESTING AND PROCEDURESMODE DESCRIPTION
1993 Geo Prizm L4-1600cc 1.6L DOHC
Mode Description
1993 Geo Prizm L4-1600cc 1.6L DOHCSECTION Mode Description
SCAN TOOL MODES
The scan tool can be used in three different modes: the normal or open mode, the special (10K) mode, and the factory test back-up or 3.9K mode. Most scan tools are programmed so that the system will enter the special (10K) mode directly, and the "normal" or "factory test" modes must be selected manually, if available.
SPECIAL (10K) MODE
In the special (10K) mode, all information incorporated into an engine/computer combination is available. However, in the special (10K) mode, engine operating characteristics are modified as follows: The closed loop timers are bypassed, Electronic Spark Timing (EST) spark is at full advance, the Idle Air Control (IAC) (if equipped) controls idle speed at 1000 RPM, the park/neutral restrict functions are disabled, and on some engines the canister purge solenoid is activated.
NORMAL (OPEN) MODE
Although not all engine/computer "families" are able to transmit information on the serial data line with the scan tool in the normal (open) mode, on engines that can be monitored in the open mode, the scan tool allows data on certain operating parameters to be obtained without changing engine operating characteristics.
FACTORY TEST
Selecting the factory test or back-up mode causes the computer to operate in the fuel back-up logic, which is designed to allow system operation in the event of an computer failure. While the selection of this mode verifies that the back-up program is functioning properly, parameters that can be checked with the tool in this mode are of little value in diagnosing system malfunctions.
The scan tool can be used in three different modes: the normal or open mode, the special (10K) mode, and the factory test back-up or 3.9K mode. Most scan tools are programmed so that the system will enter the special (10K) mode directly, and the "normal" or "factory test" modes must be selected manually, if available.
SPECIAL (10K) MODE
In the special (10K) mode, all information incorporated into an engine/computer combination is available. However, in the special (10K) mode, engine operating characteristics are modified as follows: The closed loop timers are bypassed, Electronic Spark Timing (EST) spark is at full advance, the Idle Air Control (IAC) (if equipped) controls idle speed at 1000 RPM, the park/neutral restrict functions are disabled, and on some engines the canister purge solenoid is activated.
NORMAL (OPEN) MODE
Although not all engine/computer "families" are able to transmit information on the serial data line with the scan tool in the normal (open) mode, on engines that can be monitored in the open mode, the scan tool allows data on certain operating parameters to be obtained without changing engine operating characteristics.
FACTORY TEST
Selecting the factory test or back-up mode causes the computer to operate in the fuel back-up logic, which is designed to allow system operation in the event of an computer failure. While the selection of this mode verifies that the back-up program is functioning properly, parameters that can be checked with the tool in this mode are of little value in diagnosing system malfunctions.
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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.