Failure Description and Diagnostic Test Referal

FUEL CONTROL
Fuel delivery is controlled by the control module system.
The diagnosis of fuel control starts with Chart A-3 Engine Cranks But Will Not Run. Related Tests, Information and Procedures
This chart will test the fuel system and if there is a problem, will lead you to checking the fuel pump relay circuit, diagnosing the injector circuit or diagnosing the fuel system.

Fuel Injector
Testing the fuel injector circuit is in Chart A-3 with additional diagnosis in Charts A-4, A-7 and A-8. Chart A-4 Injector Circuit Diagnosis
A fuel injector/poppet nozzle which does not open may cause a "no start" condition. An injector/poppet nozzle which is stuck partly open could cause loss of pressure after sitting so long crank times would be noticed on some engines. Also, dieseling could occur because some fuel could be delivered to the engine after the key is turned "OFF."

Pressure Regulator
Testing the pressure regulator circuit is in Charts A-3 and A-6. Related Tests, Information and Procedures Related Tests, Information and Procedures
If the pressure regulator in the fuel injection unit supplies pressure which is too low, poor performance could result. If the pressure is too high, unpleasant exhaust odor may result.

Idle Air Control (IAC)
The diagnosis of Idle Air Control (IAC) can be found in Idle Air Control System Check. System Check - Idle Air Control (IAC )
If the IAC valve is disconnected or connected with the engine running, the idle RPM may be wrong. The IAC valve may be reset by disconnecting negative battery terminal for 10 seconds then reconnect battery cable, turn ignition "ON," engine "OFF" for 5 seconds then turn ignition "OFF" for 10 seconds.
The IAC valve affects the idle characteristics of the engine. If it is open fully, too much air will be allowed in the manifold and idle speed will be high. If it is stuck closed, too little air will be allowed in the manifold and idle speed will be too low. If it is stuck part way open, the idle may be rough, and will not respond to engine load changes.

Fuel Pump Circuit
Diagnostic Trouble Code (DTC) 54 indicates a failure in the fuel pump circuit. Powertrain Controls - ECM/PCM
The fuel pump relay has a connector pigtail located near the relay to assist in testing the system. By applying voltage at this terminal, it can be determined if the fuel pump will operate. This terminal will also prime the fuel line to the TBI/CMFI unit.
Refer to Chart A-5 Fuel Pump and Relay Electrical Test for diagnosis of the fuel pump relay circuit. Chart A-5 Fuel Pump and Relay Electrical Test
An inoperative fuel pump will cause a "no start" condition. A fuel pump which does not provide enough pressure can result in poor performance.
An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold. The oil pressure switch will turn "ON" the fuel pump, as soon as oil pressure reaches about 28 kPa (4 psi).

ENGINE COOLANT TEMPERATURE (ECT) SENSOR
Diagnostic Trouble Code (DTC) 14 or 15 indicates a failure in the engine coolant temperature sensor circuit.
Most scan tools display engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90° C then stabilize when thermostat opens. Powertrain Controls - ECM/PCM Powertrain Controls - ECM/PCM

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
Diagnostic Trouble Code (DTC) 33 or 34 indicates a failure in the MAP sensor circuit. Powertrain Controls - ECM/PCM Powertrain Controls - ECM/PCM
Also refer to Manifold Absolute Pressure Output Check to check the MAP sensor if there is no DTC. MAP Sensor Output Diagnosis

HEATED OXYGEN SENSOR (O2S)
Diagnostic Trouble Code (DTC) 13 indicates an open in the Oxygen Sensor (O2S) circuit. DTC 44 indicates a low voltage in the Oxygen Sensor (O2S) circuit. DTC 45 indicates a high voltage in the Oxygen Sensor (02S) circuit. If a DTC is set, the engine will always run in the "Open Loop" mode. On heated oxygen sensors value will drop lower towards 0 as the sensor heater inside the sensor warms up.
Normal scan voltage varies between 100 mV to 999 mV (0.1 and 1.0 volt) while in "Closed Loop." DTC 13 sets in one minute if voltage remains between 0.35 and 0.55 volt, but the system will go "Open Loop" in about 15 seconds. Powertrain Controls - ECM/PCM Powertrain Controls - ECM/PCM Powertrain Controls - ECM/PCM
Using the scan tool, observe the long term fuel trim values at different RPM and air flow conditions to determine when DTC 44 or DTC 45 may have been set. If the condition for DTC 44 exists, the long term fuel trim values will be around 150. If the condition for DTC 45 exists, the long term fuel trim values will be around 115.
If the heated oxygen sensor pigtail wiring, connector or terminal is damaged, the entire oxygen sensor assembly must be replaced. Do not attempt to repair the wiring, connector or terminals. In order for the sensor to function properly, it must have provided to it a clean air reference. This clean air reference is obtained by way of the oxygen sensor signal and heater wires. Any attempt to repair the wires, connectors or terminals could result in the obstruction of the air reference and degraded oxygen sensor performance.

THROTTLE POSITION (TP) SENSOR
When a Diagnostic Trouble Code (DTC) 21 or 22 is set, the PCM will use an artificial value for throttle position and some engine performance will return. Powertrain Controls - ECM/PCM Powertrain Controls - ECM/PCM
A broken TP sensor can cause intermittent bursts of fuel from the injector(s) and an unstable idle because the PCM thinks the throttle is moving.
A scan tool reads throttle position in volts and should read about 0.60 volt with the throttle closed, ignition "ON" or at idle. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT).
Scan TP signal while depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from below 0.85 volt (850 mV) when throttle was closed, to over 4.5 volts (4500 mV) when throttle is held at wide open throttle position.

TP Sensor Output
This check should be performed when TP sensor attaching parts have been replaced. A Tech 1 scan tool can be used to read the TP signal output voltage, or:
1. Connect digital voltmeter J 39200 or equivalent, from TP sensor connector terminal "B" (BLK wire) to terminal "C" (DK BLU wire). Jumpers for terminal access can be made using terminals "1214836" and "12014837".
2. With ignition "ON," engine stopped, the TP sensor voltage should be less than 0.85 volt if more than 0.85 volt verify free throttle movement. If still more than 1.25 volts, replace TP sensor.
3. Remove the voltmeter and jumpers, reconnect the TP sensor connector to the sensor.

VEHICLE SPEED SENSOR (VSS)
The vehicle speed sensor circuit diagnosis is in the DTC 16 or 24 chart. DTC 16
Scan tool reading should closely match speedometer readings, with the drive wheels turning.

EGR SYSTEM
Diagnostic Trouble Code (DTC) 32 indicates that there is a failure in the EGR system circuit. Powertrain Controls - ECM/PCM

IDLE SPEED
Refer to Idle Air Control System Check. System Check - Idle Air Control (IAC )
^ System too lean (high air/fuel ratio) - Idle speed may be too high or too low. Engine speed may vary up and down, disconnecting IAC does not help. May set DTC 44. Scan tool or voltmeter will read an oxygen sensor output less than 300 mV (0.3 volt). Check for low regulated fuel pressure or water in fuel. A lean exhaust with an Oxygen Sensor (O2S) output fixed above 800 mV (0.8 volt) will be a contaminated sensor, usually silicone. This may also set a DTC 45.
^ System too rich (low air/fuel ratio) - Idle speed too low. Scan counts usually above 80. System obviously rich and may exhibit black exhaust smoke. Scan tool and/or voltmeter will read an Oxygen Sensor (02S) signal fixed above 800 mV (0.8 volt).

IGNITION CONTROL (IC)
When the system is running on the ignition control module, that is, no voltage on the bypass line, the ignition control module grounds the Ignition Control (IC) signal. The PCM expects to see no voltage on the IC line during this condition. If it sees a voltage, it sets DTC 42 and will not go into the IC mode. Powertrain Controls - ECM/PCM
When the RPM for IC is reached (about 400 RPM), and bypass voltage is applied, the IC should no longer be grounded in the ignition control module so the IC voltage should be varying.
If the bypass line is open or grounded, the ignition control module will not switch to IC mode so the IC voltage will be low and DTC 42 will be set.
If the IC line is grounded, the ignition control module will switch to IC, but because the line is grounded there will be no IC signal. A DTC 42 will be set.
DTC 42 sets if there is an open or a short to ground in the IC or bypass circuit.

KNOCK SENSOR (KS) SYSTEM
DTC 43 sets if there is an open or short to ground in the circuit.
If the conditions for DTC 43 are present, the scan will always display "YES." There should not be a knock at idle unless an internal engine problem, or a system problem exists. Powertrain Controls - ECM/PCM

SYSTEM OVER VOLTAGE
DTC 53 sets if there is voltage greater than 17.1 volts for two seconds at PCM terminal "E16." This indicates that there is a basic generator problem. Powertrain Controls - ECM/PCM

INTAKE MANIFOLD TUNING VALVE ASSEMBLY
Refer to Intake Manifold Tuning Valve Diagnostic Chart.

IGNITION REFERENCE SIGNAL
The ignition reference signal is covered in the Distributor Ignition System Check System Check - Distributor Ignition (DI)

A/C SIGNAL
Refer to A/C Signal Diagnosis.

EXHAUST SYSTEM
Refer to Restricted Exhaust System Check. System Check - Restricted Exhaust