Engine Controls - System & Component Testing: Overview Isuzu Axiom I

Test Description

Numbers below refer to the numbers in the Diagnostic Procedure

1. 1 Check to see if solenoid is open or closed. Solenoid is normally de-energized in this step.
2. 2 This step checks to determine if the solenoid was open due to an electrical circuit problem or a defective solenoid.
3. 3 This should normally energize the solenoid, opening the valve and allowing vacuum to drop (purge On).

System Description

Fuel evaporative system operation is monitored by PCM. Engine vacuum is applied to system and monitored for leakage. PCM monitors vacuum in EVAP system with Fuel Vapor Pressure (FVP) sensor. Amount of engine vacuum is controlled by the EVAP Purge and Vent solenoid valves. If a specific amount of vacuum cannot be achieved or maintained, PCM will set DTC. Inspect above listed components for poor, loose or damage to terminal connections.

1. 2 Relieve fuel pressure by connecting Fuel Pressure Gauge (J34730-1) or equivalent to fuel pressure connection on fuel rail. Place fuel pressure gauge bleed hose in an approved gasoline container. With ignition off, open valve on fuel pressure gauge.
2. 3 Record lowest voltage displayed by DVOM after first second of test. (During first second, voltage displayed by DVOM may be inaccurate due to initial current surge). Voltage displayed by DVOM should be within specified range. Voltage displayed by DVOM may increase throughout test as fuel injector windings warm and resistance of fuel injector windings changes. An erratic voltage reading (large fluctuations in voltage that do not stabilize) indicates an intermittent connection within fuel injector. FUEL INJECTOR SPECIFICATIONS Resistance Ohms Voltage Specification (1) 11.8-12.6 5.7-6.6 (1) Resistance should be taken with engine coolant between 50°F-95°F (10°C-35°C).
3. 5 Injector Specifications: FUEL INJECTOR SPECIFICATIONS Highest Acceptable Voltage Reading Above/Below 95/50°F (35/10°C) Acceptable Subtracted Value 9.5 Volts 0.6 Volts

Numbers below refer to the numbers in the Diagnostic Procedure

1. 1 IAC motor analyzer (J39027-A) is used to extend and retract IAC valve. Valve movement is verified by a change in engine speed. If no change in engine speed occurs, IAC valve can be resettled when removed from throttle body.
2. 2 This step checks quality of IAC movement in step 1 . Between 700-1500 RPM, engine speed should change smoothly with each flash of test light in both extend and retract directions. If IAC valve is retracted beyond control range (about 1500 RPM), it may take many flashes to extend IAC valve before engine speed will begin to drop. This is normal on certain engines. Fully extending IAC may cause engine to stall and may be considered normal.
3. 6 Steps 1 and 2 , verified proper IAC valve operation. This step checks IAC circuits. Each lamp on noid light should flash red and green while IAC valve is cycled. While sequence of color is not important, if either light is OFF or does not flash red and green, check IAC circuits for faults, beginning with poor terminal contacts.

Numbers below refer to the numbers in the Diagnostic Procedure

1. 3 This test determines is problem is with refrigerant system. If switch is open, A/C pressure gauges will be used to determine if pressure switch is faulty or if the system is partially discharged or empty.
2. 4 Although the normal complaint will be A/C clutch fails to engage, it is possible for a short circuit to cause A/C clutch to run when A/C has not been selected. This step tests for that condition.
3. 7 There is an extremely low probability that both relays will fail at the same time, so substitution process is one way to check A/C Thermostat relay. Use a known good relay to do a substitution check.

MISFIRE MONITOR DIAGNOSTIC OPERATION

Misfire is monitored as a function of the Combustion Quality (CQ) signals generated from the ignition current sense system. Combustion signals represent degree of combustion in each cylinder. Misfire is detected when combustion signal is below a predetermined value. Misfire ratio is calculated once every 100 engine cycles. For example, on a 6-cylinder engine, 600 ignition plug sparks occur every 100 cycles and if a misfire occurs 12 times during that time, the misfire ratio is 12/600 x 100 = 2%.

FUEL TRIM SYSTEM MONITOR DIAGNOSTIC OPERATION

Fuel trim system monitors the averages of short-term and long-term fuel trim values. If fuel trim values stay at their limits for a calibrated period of time, a malfunction is indicated. The fuel trim diagnostic compares averages of short-term fuel trim values and long-term fuel trim values to rich and lean thresholds. If either value is within the thresholds, a pass is recorded. If both values are outside their thresholds, a rich or lean DTC will be recorded. Fuel trim system diagnostic also conducts an intrusive test. This test determines if a rich condition is being caused by excessive fuel vapor from the EVAP canister. To meet OBD-II requirements, the PCM uses weighted fuel trim cells to determine need to set a fuel trim DTC. A fuel trim DTC can only be set if fuel trim counts in weighted fuel trim cells exceed specifications. This means that vehicle could have a fuel trim problem which is causing a problem under certain conditions (i.e., engine idle high due to a small vacuum leak or rough idle due to a large vacuum leak), while it operates fine at other times. No fuel trim DTC would set (although an engine idle speed DTC or Heated Oxygen Sensor DTC may set). Use scan tool to observe fuel trim counts while problem is occurring. A fuel trim DTC may be triggered by a number of vehicle faults. Make use of all information available (other DTCs stored, rich or lean condition, etc.) when diagnosing a fuel trim fault.

See also:
• WIRING DIAGRAMS
• SELF-DIAGNOSTICS - AXIOM 3.5L, PASSPORT, RODEO & RODEO SPORT 3.2L