Tracker 4WD V6-2.5L VIN 4 (2001)
Accessory Signal: Testing and Inspection
ELECTRICAL/ACCESSORY LOAD IDLE-UP SIGNAL DIAGNOSIS
CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) receives an idle-up signal when certain engine electrical loads or engine accessory loads are present. The
PCM increases the flow of air through the idle (bypass) air passage of the Idle Air Control (IAC) valve when receiving an idle-up signal. The
additional air flowing through the idle air passage causes an increase in the idle speed. The idle speed is increased in order to accommodate the
increased engine electrical or engine accessory load. The PCM monitors the following systems for idle-up signals:
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The exterior lighting system
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The HVAC system blower motor
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The electric rear window defogger
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The A/C system-When A/C is selected from the HVAC control unit the A/C compressor control module sends an A/C On signal to the PCM. Once
the PCM is aware of the request for A/C, the PCM will determine whether engagement of the A/C compressor clutch is OK. The A/C compressor
control module requires a signal from the PCM in order to allow operation of the A/C compressor. The A/C compressor control module will not
turn on the A/C compressor clutch relay unless the PCM pulls the A/C Cutout Control circuit low. The increase in the idle speed prevents a rough
idle or a stalling condition when the A/C compressor is engaged.
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The power steering system-The Power Steering Pressure (PSP) switch is normally open to ground. Turning the steering wheel increases the power
steering oil pressure. Increased power steering oil pressure puts an additional load on the engine that may be noticeable at idle. The PSP switch
closes when the power steering system oil pressure is high enough to cause an undesirable idle condition. The voltage signal from the PSP switch
to the PCM indicates less than one volt when the PSP switch is closed. The voltage signal is near battery voltage when the PSP switch is open.
DIAGNOSTIC AIDS
Check for any of the following conditions:
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The High Electrical Load parameter on the scan tool can indicate if the PCM has received the rear defogger or parking lamps ON signal. The scan
tool should indicate Yes when the rear defogger or parking lamps are turned ON and engine speed should increase slightly. Check for a
malfunction in the IAC system or a short to ground in the Diagnostic Request circuit if the engine speed does not increase.
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A malfunctioning parking lamp (taillight) circuit may cause erratic performance of the electrical load idle-up circuit.
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A PSP switch that is shorted can cause the engine idle speed to remain high even when driving straight ahead.
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A PSP switch that is incorrectly calibrated can cause the engine idle speed to remain low when steering pump hydraulic pressure is high.
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A faulty ground in the PSP switch can cause erratic switch operation. Inspect that the PS pump and bracket are secure, insuring a good path to
ground. Inspect the PSP switch for a tight installation.
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The scan tool will display A/C Relay Command On when the air conditioning control is turned ON, the blower switch is also ON, and the A/C
compressor is operating.
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Observe the IAC Motor Command on a scan tool while operating the A/C. The IAC Motor Command percentage should increase 4 to 12 percent
when the A/C compressor is engaged. If the scan tool indicates that the IAC Duty Cycle is increasing, but the idle quality is unsatisfactory, inspect
the IAC system for proper operation.
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If the scan tool indicates that the IAC Motor Command is increasing, but the idle quality is unsatisfactory, inspect the IAC system for proper
operation. Refer to Idle Air Control (IAC) System Diagnosis. See: Testing and Inspection/Component Tests and General Diagnostics
An intermittent malfunction may be caused by a fault in any one of the idle-up circuits. Inspect the wiring harness and components for an intermittent
condition. Refer to Intermittent Conditions. See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Strategies/Intermittent
Conditions
TEST DESCRIPTION