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
Numbers below refer to the step numbers on the Diagnostic Table:
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Determines if the ignition control module (ICM) is receiving the 18X CKP Reference signal. If the 18X CKP signal to the ICM is not present, there will be no RPM, spark, or fuel injector pulses.
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Ensures that the ICM has the proper voltage supply and ground.
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Verifies that the ICM is supplying the proper sensor feed voltage.
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Check for the proper operation of the CKP Sync signal, ICM and related spark system components. Without the CKP Sync signal the ICM is unable to properly sequence the ignition coils.
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If the 18X and CKP Sync signals to the ICM or the 18X and 3X reference signals to the ICM short together the vehicle will not start and run. However, there will be spark and fuel injector pulses.
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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 | Values | 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 DTCs are stored as failed since code clear, diagnose the DTCs before continuing with this table.
Was a problem found? | -- | ||||||||||||||||||
3 |
Is the fuel pressure within the specified values and holding? | 333-376 kPa (48-55 psi) | ||||||||||||||||||
4 | Is any fuel pressure indicated? | -- | ||||||||||||||||||
Does the scan tool indicate an engine RPM? | -- | |||||||||||||||||||
Is the test lamp ON? | -- | |||||||||||||||||||
7 |
Is the test lamp ON? | -- | ||||||||||||||||||
Does the DMM display a voltage near the specified value? | B+ | |||||||||||||||||||
9 | Connect the DMM between the 18X CKP sensor signal and sensor ground terminals in the connector. Does the DMM display a voltage in the specified range? | 6-9V | ||||||||||||||||||
10 |
Was a problem found? | -- | ||||||||||||||||||
11 | Connect the DMM between the 18X CKP sensor feed and engine ground. Does the DMM display a voltage near the specified value? | B+ | ||||||||||||||||||
12 |
Was a problem found? | -- | ||||||||||||||||||
13 |
Was a problem found? | -- | ||||||||||||||||||
14 |
Does the DMM display a voltage? | -- | ||||||||||||||||||
15 | Locate and repair the short to voltage. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |||||||||||||||||
16 |
Was a problem found? | -- | ||||||||||||||||||
17 |
Was the injector test lamp ON for any of the injectors? | -- | ||||||||||||||||||
18 |
Was the test lamp ON for any of the injectors? | -- | ||||||||||||||||||
19 |
Did the injector test lamp blink for each injector? | -- | ||||||||||||||||||
20 | Did the injector test lamp blink for any of the injectors? | -- | ||||||||||||||||||
21 |
Was a problem found? | -- | ||||||||||||||||||
22 |
Is the test lamp ON? | -- | ||||||||||||||||||
23 | Locate and repair the open ignition positive feed circuit to the fuel injectors. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |||||||||||||||||
Is spark available at all cylinders? | -- | |||||||||||||||||||
25 | Is spark available at any cylinder? | -- | ||||||||||||||||||
26 |
Does the DMM display a voltage near the specified value? | 6-9V | ||||||||||||||||||
27 | Check for poor terminal connections at the 18X CKP sensor. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems. Was a problem found? | -- | ||||||||||||||||||
28 |
Was a problem found? | -- | ||||||||||||||||||
29 |
Was a problem found? | -- | ||||||||||||||||||
30 |
Refer to Spark Plug Wire Harness Replacement .
Was a problem found? | -- | ||||||||||||||||||
31 |
Was a problem found? | 5K-8K ohms (5000 - 8000 ohms) | ||||||||||||||||||
32 |
Was a problem found? | 3280-4921 ohms per meter (1000-1500 ohms per ft | ||||||||||||||||||
33 |
Does the test lamp blink continuously while the engine is being cranked? | -- | ||||||||||||||||||
34 |
Did the spark plug inspection reveal excessive fouling? | -- | Go to Base Engine Misfire Diagnosis | |||||||||||||||||
Refer to Diagnostic Aids to check for the following conditions:
Was a problem found? | -- | |||||||||||||||||||
36 | Test the fuel for contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . If a problem is found, clean the fuel system and correct the contaminated fuel conditions as necessary. Was a problem found? | -- | ||||||||||||||||||
37 |
Is action complete? | -- | -- | |||||||||||||||||
38 |
Was a problem found? | -- | ||||||||||||||||||
39 | Locate and repair the open in the ICM ground circuit. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |||||||||||||||||
40 | Locate and repair the open in the ignition positive feed circuit to the ICM. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |||||||||||||||||
41 | Replace the 18X CKP sensor. Refer to Crankshaft Position Sensor Replacement . Is action complete? | -- | -- | |||||||||||||||||
42 | Replace the ICM. Refer to Ignition Control Module Replacement Is action complete? | -- | -- | |||||||||||||||||
43 | Locate and repair the short to ground in the fuel injector control circuits associated with the injector test lamps that stayed ON. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |||||||||||||||||
44 | Check for poor terminal connections at the PCM. If a problem is found, repair as necessary. Refer to Repairing Connector Terminals in Wiring Systems. Was a problem found? | -- | ||||||||||||||||||
45 | Replace the ignition coils associated with the cylinders that did not have spark. Refer to Ignition Coil Replacement . Is action complete? | -- | -- | |||||||||||||||||
|
Important: Replacement PCM must be reprogrammed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- |
