Diagnostic Aids: Overview

Normal scan tester voltage varies between .1-1.0 volt while in closed loop. Code 13 sets in approximately 40 seconds if voltage remains between .35 and .55 volt, but system will enter open loop in approximately 15 seconds. For intermittent inspection, see TESTS W/O CODES article.

Fig 1: Code 13 - Schematic

Courtesy of ISUZU MOTOR CO.

Fig 2: Code 13 - Diagnostic Flowchart (1 Of 2)

Courtesy of ISUZU MOTOR CO.

Fig 3: Code 13 - Diagnostic Flowchart (2 Of 2)

Courtesy of ISUZU MOTOR CO.

After engine is started, temperature should rise steadily to approximately 194°F (90°C), and then stabilize when thermostat opens. When a Code 14A is set, ECM will turn on engine cooling fan. Code 14A will set if circuit No. D12 is shorted to ground. For intermittent inspection, see TESTS W/O CODES article.

Fig 1: Code 14A - Schematic

Courtesy of ISUZU MOTOR CO.

Fig 2: Code 14A - Diagnostic Flowchart

Courtesy of ISUZU MOTOR CO.

After engine is started, temperature should rise steadily to approximately 194°F (90°C), then stabilize when thermostat opens. Code 14B will set if circuits No. A11 and D12 are open. Check terminals at sensor for good contact. For intermittent inspection, see TESTS W/O CODES article.

Fig 1: Code 14B - Schematic

Courtesy of ISUZU MOTOR CO.

Fig 2: Code 14B - Diagnostic Flowchart

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A scan tester reads throttle position in volts. With ignition on, reading should be less than one volt with throttle closed. Voltage should increase at a steady rate as throttle is moved toward WOT. An open or short to ground in circuits No. A1 or D6 will cause Code 21B to set. For intermittent inspection, see TESTS W/O CODES article.

Fig 1: Code 21B - Schematic

Courtesy of ISUZU MOTOR CO.

Fig 2: Code 21B - Diagnostic Flowchart

Courtesy of ISUZU MOTOR CO.