Information Sensors/Switches Part 2
Part 2
Throttle Position Sensor
The Throttle Position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body. By monitoring the voltage on the signal line the PCM calculates throttle position. As the throttle valve angle is changed (accelerator pedal moved) the TP sensor signal also changes. At a closed throttle position, the output of the TP sensor is low. As the throttle valve opens the TP sensor voltage increases so that at Wide Open Throttle (WOT), the TP sensor voltage should be above 4 volts. The PCM calculates fuel delivery based on throttle valve angle (driver demand).
A broken or loose TP sensor may cause intermittent bursts of fuel from an injector and unstable idle because the PCM thinks the throttle is moving. A hard failure in the TP sensor 5 volts reference or signal circuits should set either a DTC P0122 or DTC P0123. A hard failure with the TP sensor ground circuit may set DTCs P0123 and P0117. Once a DTC is set, the PCM will use an artificial default value based on engine RPM and mass air flow for throttle position and some vehicle performance will return. A high idle may result when either DTC P0122 or DTC P0123 is set.
The PCM can detect intermittent TP sensor faults. DTC P1121 or DTC P1122 will set if an intermittent high or low circuit failure is being detected. The PCM can also detect a shifted TP sensor. The PCM monitors throttle position and compares the actual TP sensor reading to a predicted TP value calculated from engine speed. If the PCM detects an out of range condition, DTC P0121 will be set.
Transaxle Range Switch
The Transaxle Range Switch is part of the Transaxle Park/Neutral Position (PNP) switch mounted on the transaxle manual shaft. The 4 inputs from the transaxle range switch indicate to the PCM which position is selected by the Transaxle selector lever. This information is used for transmission shift control, ignition timing, EVAP canister purge, EGR and IAC valve operation. The combination of the four transaxle range input states determine the PCM commanded shift pattern. The input voltage level at the PCM is high (B+) when the transaxle range switch is open and low when the switch is closed to ground. The state of each input is represented on the scan tool as High voltage level, Low voltage level. The four parameters represent transaxle range switch Parity, A B, and C inputs respectively. Valid transaxle range input combinations are shown in the Transaxle Range Switch Valid Input Combinations table.
Transaxle Range Switch Valid Input Combinations
PCM Controlled Air Conditioning
The air conditioning system uses a variable displacement compressor referred to as type V-5. The V-5 compressor meets A/C requirements without cycling. The A/C compressor operation is controlled by the Powertrain Control Module (PCM) for the following reasons:
^ Improved idle quality during compressor clutch engagement.
^ Improved wide open throttle performance (WOT).
^ Protects the A/C compressor from operation with incorrect refrigerant pressures.
The A/C clutch electrical system consists of the following components:
^ The A/C control head and/or the A/C programmer.
^ The A/C refrigerant pressure sensor.
^ The A/C compressor clutch.
^ The A/C compressor clutch relay.
^ The PCM.
When an A/C mode is selected, the A/C control head/programmer sends the A/C request signal to the PCM. The A/C compressor clutch relay is controlled by the PCM. The PCM provides a ground path for the A/C relay coil. The PCM will enable the A/C compressor clutch relay whenever the engine is running and the A/C has been requested by the A/C control head/programmer. When the A/C compressor relay is engaged, battery voltage is supplied to the compressor clutch coil. The PCM and the A/C control head/programmer monitor the A/C pressure sensor signal. If the A/C pressure sensor signal indicates an A/C pressure outside the normal operation range, the A/C control head/programmer will remove the A/C request signal from the PCM. The PCM will disengage the A/C relay.
The PCM will enable the A/C relay unless one or more of the following conditions are present:
^ Throttle angle is greater than 96%.
^ A/C head pressure is greater than 440 psi (4.6 volts) or less than 35 psi (0.4 volt) as determined by the A/C refrigerant pressure sensor.
^ Ignition voltage is less than 10.5 volts.
^ Engine speed is greater than 5400 RPM for any amount of time.
^ Engine speed is greater than 4300 RPM for longer than 1 second.
^ ECT is greater than 124°C (255°F).
^ IAT is less than 5°C (41°F).
Any of the conditions described above will inhibit A/C compressor relay operation.
Diagnosis
DTC P0530, P0560, P1639, or P1641 can affect A/C operation. Refer to the DTC tables if any DTCs are set.
The PCM Controlled Air Conditioning Diagnosis table diagnoses the electrical portion of the A/C compressor clutch circuit. To diagnose the refrigerant portion of the HVAC system, refer to the Heater, Ventilation, and Air Conditioning. A scan tool will be used in diagnosing the system. The scan tool displays the A/C request and refrigerant pressure inputs to the PCM. The scan tool displays the PCM commanded state of the A/C clutch. The scan tool can override the A/C request signal and energize the A/C control relay.
Engine Cooling Fan Description - Electric Operation
The engine cooling fans receive power from separate maxifuses located in the Underhood Electrical Center. During low speed operation, the PCM supplies a ground path for the Cool Fan 1 relay through the Low Speed Fans control circuit. This energizes the relay coil, closes the Fan 1 relay contacts, and supplies current from the 40 amp maxifuse to the engine cooling fans. Engine Coolant Fan #1 grounds through the series/parallel cooling fan relay (Cool Fan 2 Relay) and Engine Coolant Fan #2. This creates a series circuit with both fans running at low speed.
To command high speed cooling fan operation, the PCM first supplies a ground path for the low speed cooling fan (Cool Fan 1) relay through the Low Speed Fans Control circuit. After a 3 second delay, the PCM supplies a ground path for the Cool Fan 2 Relay and the Cool Fan #3 relays through the High Speed Fans Control circuit. Engine Coolant Fan #1 continues to receive current from the 40 amp maxifuse. However, a 30 amp maxifuse supplies current to Engine Coolant Fan #2. Each fan receives a separate path to ground. Therefore, the fans operate at high speed.
Important: When certain Diagnostic Trouble Codes (DTCs) set, the PCM may command the cooling fans to run all the time. It is important to perform the Powertrain On-Board Diagnostic System check prior to diagnosing the engine cooling fans. Testing and Inspection
The PCM completes the ground path for Cool Fan 1 relay under any of the following conditions:
^ When engine coolant temperature exceeds 106°C (223°F).
^ When A/C is requested and ambient temperature is greater than 50°C (122°F).
^ When A/C refrigerant pressure is greater than 190 psi (2 volts).
^ When the ignition is off and engine coolant temperature is greater than 140°C (284°F).
For high speed operation, the PCM delays control of the Cool Fan 2 and Cool Fan 3 relays for 3 seconds. The 3 second delay ensures that cooling fan electrical load does not exceed the capacity of the system. The PCM completes the ground paths for Cool Fan 1, Cool Fan 2 and Cool Fan 3 relays under any of the following conditions:
^ When engine coolant temperature exceeds 110°C (230°F).
^ When A/C refrigerant pressure is greater than 240 psi (2.5 volts).
Diagnosis
DTC P1651 should set if a problem occurs which affects the low speed fans control circuit. If the problem affects the high speed fans control circuit, DTC P1652 should set. A problem with the ECT sensor should set DTC P0117, P0108, P1114, or P1115. Any of these DTCs will affect cooling fan operation. Therefore, diagnose any ECT DTCs before using the Electric Cooling Fan Diagnosis table. If no DTCs set and a cooling fan problem exists, use the Electric Cooling Fan Diagnosis to diagnose the PCM controlled cooling fans.