Fuel Injector Circuit Diagnosis

Diagnostic Chart:

Schematic:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) controls each individual fuel injector sequentially. The PCM energizes the solenoid coil of the fuel injectors. When energized the fuel injector solenoid operates the solenoid plunger allowing pressurized fuel to be injected into the intake port of the cylinder. The fuel pump will pressurize the fuel rail and the fuel injectors as long as the engine is cranking, and the PCM is receiving ignition system reference pulses. The fuel pump will stop after 2 seconds if the PCM does not receive any ignition system reference pulses. The PCM depends on crankshaft position sensor and camshaft position sensor inputs in order to determine when to energize the fuel injectors. The PCM depends primarily on engine speed and information sensor inputs in order to determine how long to energize the fuel injectors.

DIAGNOSTIC AIDS
Check for any of the following conditions:
^ Water, contaminated fuel, or inferior quality fuel can cause a no start or hard start condition even though the fuel injectors and circuitry are OK.
^ Check for a faulty spray pattern from the fuel injector nozzle if both the fuel injector solenoid and the fuel injector circuit are OK.
^ A leaking or stuck closed (blocked) fuel injector can cause a fuel related engine misfire or performance concern. Refer to Fuel Injector Balance Test (SFI) in order to check the operation of the fuel injectors. Component Tests and General Diagnostics
^ The fuel injectors may spray fuel, but not enough fuel to operate the engine. Check the Engine Coolant Temperature (ECT) sensor reading with a scan tool. The indicated temperature should be close to the actual engine temperature in order for the PCM to deliver the correct amount of fuel.
^ Normal fuel injector resistance is 12-13 ohms at 20°C (68°F). Refer to Fuel In] Coil Test - ECT Between 10-35 Degrees C (50-95 Degrees F). Component Tests and General Diagnostics
^ Inspect the camshaft timing belt for proper installation and operation. An engine with no injector pulse on two injectors while cranking the engine may have incorrect valve timing. Incorrect valve timing can affect the phasing of the CKP sensor and CMP sensor signals, resulting in no fuel injector pulse to the fuel injectors.

An intermittent malfunction may be caused by a fault in the fuel injector electrical circuit. Inspect the wiring harness and components for any of the following conditions:
^ Backed out terminals.
^ Improper mating of terminals.
^ Broken electrical connector locks.
^ Improperly formed or damaged terminals.
^ Faulty terminal to wire connections.
^ Physical damage to the wiring harness.
^ Broken conductor inside the wire insulation.
^ Corrosion of electrical connections, splices, or terminals.

TEST DESCRIPTION
The numbers below refer to the step numbers in the diagnostic table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks, and to save the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data that was taken when the fault occurred. The scan tool saves the information for later reference.
2. This step checks if the PCM is controlling the fuel injector signals.
3. This step checks for a short in the fuel injector control circuit.
5. This step checks for voltage at the fuel injector.
6. This step checks for an open in the fuel injector control circuit or for a faulty PCM.