Circuit Description
The electronic ignition system uses a waste spark method of spark distribution. In this type of ignition system, the ignition control module triggers the correct coil based on the sync signal received from the crankshaft position sensor, resulting in both spark plugs connected to the coil firing at the same time. The spark plug for the cylinder on the exhaust stroke requires a lower energy requirement in order to fire, leaving the remaining high voltage to fire the spark plug for the cylinder on the compression stroke.
During crank, the ignition control module monitors the crankshaft position (CKP) sync signal. The CKP sync signal is used to determine the correct cylinder pair to fire first. The CKP sync signal is used only by the ignition control module in order to initiate the ignition coil firing sequence. It is not passed to the PCM. After the ignition control module processes the CKP sync signal, the ignition control module monitors the 18X CKP signal and sends 18X and 3X reference pulses to the PCM. When the PCM receives these pulses, the PCM will command all six injectors in order to allow a priming shot of fuel for all the cylinders. After the priming, the injectors are left OFF during the next six 3X reference pulses from the ignition control module. This allows each cylinder a chance to use the fuel from the priming shot. During this waiting period, the PCM receives a camshaft position signal pulse. The camshaft position signal allows the PCM to operate the injectors sequentially, based on camshaft position. If the camshaft position signal is not present at start-up, the PCM will begin sequential fuel delivery with a 1 in 6 chance that fuel delivery is correct.
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed-through wire insulation, or a wire broken inside the insulation. Check for the following items:
| • | A shorted camshaft position sensor |
| An internally-shorted camshaft position sensor can cause an Engine Cranks but Will not Run condition. If the diagnostic table indicates a short to ground in the sensor ignition positive voltage circuit, disconnect the camshaft position sensor and attempt to start the vehicle. If the vehicle starts with the camshaft position sensor disconnected, a shorted camshaft position sensor is indicated. |
| • | A poor connection or a damaged harness |
| Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connections, and a damaged harness. |
| • | A malfunctioning engine coolant temperature sensor |
| Using a scan tool, compare the engine coolant temperature with the intake air temperature on a completely cool engine. The engine coolant temperature should be within 10°C (50°F) of the intake air temperature. If it is not, replace the ECT sensor. |
| • | The throttle position (TP) sensor |
| If the TP angle is more than 80 percent, the PCM may operate in clear flood mode. The PCM will not allow fuel delivery while operating in clear flood mode. |
Test Description
Number(s) below refer to the Step number(s) on the Diagnostic Table:
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A blinking test light verifies that the PCM is monitoring the 3X and 18X reference signals and is capable of activating the injectors
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The crankshaft position sensor and fuel injectors have been verified as functioning properly. A fuel pressure test will separate the diagnostic path into either a fuel pressure related malfunction or an ignition system malfunction.
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By using a J 26792 Spark Tester to test for spark on the plug wires, each ignition coil's ability to produce at least 25,000 volts is verified.
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If any of the ignition coil towers exhibit carbon tracking, replace the ignition coil and the associated ignition wire.
If any ignition wire exhihits carbon tracking inside the boot that connects to the coil tower, replace the ignition wire and the associated coil.
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By testing the problem coil's control circuit with a test light, a determination can be made as to the problem coil malfunctioning or the ignition control module's internal control circuit for the affected coil being the cause of the condition
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An internally shorted camshaft position sensor can cause an engine cranks but will not run condition. If the diagnostic table indicates a short to ground in the sensor ignition positive voltage circuit, disconnect the camshaft position sensor and attempt to start the vehicle. If the vehicle starts with the camshaft position sensor disconnected, a shorted camshaft position sensor is indicated.
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This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||||||||||
2 |
Important:: Before proceeding with this diagnostic Table, ensure that the vehicle battery is fully charged. Important:: If any the following DTCs are stored as failed since code clear, diagnose the DTC(s) before continuing with this table:
Was a problem found? | -- | ||||||||||||||||||
3 | Observe Engine Speed display on the scan tool while cranking the engine. Is engine RPM indicated? | -- | ||||||||||||||||||
4 |
Are any of the injector test lights ON? | -- | ||||||||||||||||||
Crank the engine while monitoring the injector test lights. Do all of the injector test lights blink continuously while the engine is being cranked? (If not, record which injector test lights did not blink.) | -- | |||||||||||||||||||
Is the fuel pressure within the specified values and holding? | 333-375 kPa (48-55 psi) | |||||||||||||||||||
7 | Is any fuel pressure indicated? | -- | ||||||||||||||||||
8 |
Was a problem found? | -- | ||||||||||||||||||
Is adequate spark present at all cylinders? | -- | |||||||||||||||||||
10 |
Did your inspection reveal any spark plugs exhibiting excessive fouling? | -- | Go to Engine Mechanical Diagnosis in Engine General Information | |||||||||||||||||
11 | Is spark present at any ignition wires? | -- | ||||||||||||||||||
Was a problem found? | -- | |||||||||||||||||||
13 |
Was a problem found? | 5K-8K ohms (5000-8000 ohms) | ||||||||||||||||||
14 |
Was a problem found? | VIN 1 - 7K ohms (7000 ohms) VIN K - 10K ohms (10,000 ohms) | ||||||||||||||||||
Does the test light blink continuously while the engine is being cranked? | -- | |||||||||||||||||||
16 |
Are any of the injector test lights ON? | -- | ||||||||||||||||||
17 | Locate and repair short to ground in the injector control circuit(s) associated with the injector test light(s) that stayed ON. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||||||||
18 | Did any of the injector test lights blink continuously? | -- | ||||||||||||||||||
19 |
Is the test light ON at all of the injector connectors? | -- | ||||||||||||||||||
20 |
Was a problem found? | -- | ||||||||||||||||||
21 | Probe the fuel injector ignition positive voltage circuit at any injector connector with a test light to ground. Is the test light ON? | -- | ||||||||||||||||||
22 |
Does the injector test light blink? | -- | ||||||||||||||||||
23 |
Is the test light ON? | -- | ||||||||||||||||||
24 |
Is voltage between the specified values? | 1 V-3 V | ||||||||||||||||||
25 | Is the voltage greater than the specified value? | 3 V | ||||||||||||||||||
26 |
Was the test light ON? | -- | ||||||||||||||||||
Was a problem found? | -- | |||||||||||||||||||
28 |
Is voltage between the specified values? | 5 V-7 V | ||||||||||||||||||
29 | Is the voltage greater than the specified value? | 7 V | ||||||||||||||||||
30 |
Was the test light ON? | -- | ||||||||||||||||||
31 |
Was a problem found? | -- | ||||||||||||||||||
32 |
Was a problem found? | -- | ||||||||||||||||||
33 | Locate and repair the open in the fuel injector ignition positive voltage circuit. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||||||||
34 | Locate and repair open in the ignition control module ignition positive voltage circuit. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||||||||
35 |
Was a problem found? | -- | ||||||||||||||||||
36 | Repair the engine mechanical problem. Refer to Engine Mechanical Diagnosis in Engine General Information to diagnose the following conditions:
Is action complete? | -- | -- | |||||||||||||||||
Replace the PCM Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||||||||||||||||||
38 | Replace the ignition coil(s) associated with the cylinders that did not have spark. Refer to Ignition Control Module Replacement . Is action complete? | -- | -- | |||||||||||||||||
39 | Replace the electronic ignition control module. Refer to Ignition Control Module Replacement . Is action complete? | -- | -- | |||||||||||||||||
40 | Replace the crankshaft position sensor. Refer to Crankshaft Position Sensor Replacement Is action complete? | -- | -- |
