Circuit Description
The ignition control module (ICM) has independent power and ground circuits. The circuits between the ICM and the powertrain control module (PCM) consists of the following circuits:
| • | The ignition control (IC) timing signal |
| • | The IC timing control |
| • | The low resolution engine speed signal |
| • | The medium resolution engine signal |
| • | The camshaft position signal |
| • | The low reference |
The ICM sends 3X signals to the PCM, and controls the timing advance during engine cranking. The timing advance changes to PCM control after the following actions occur:
| • | The PCM receives the second 3X signal |
| • | The PCM applies 5 volts to the ignition control (IC) timing signal circuit. |
The ICM monitors the CKP sync signal when the engine is cranking. The CKP sync signal is passed from the CKP sensor to the ICM on the CKP sensor 2 signal circuit. The CKP sync signal is used to determine the correct cylinder pair and initiate the ignition coil firing sequence. The 18X reference pulses are passed from the CKP sensor to the ICM on the CKP sensor 1 circuit. The 18X reference pulses are used for fuel injection and ignition control. After the ICM receives both signals, the ICM passes the 18X and 3X reference signals to the PCM. The CMP and the CKP sensors share a 12 volt reference and low reference circuit. The CKP sensor consists of the following circuits:
| • | A 12 volt reference |
| • | A low reference |
| • | A CKP sensor 1 signal |
| • | A CKP sensor 2 signal |
Diagnostic Aids
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.
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:
| • | Poor connection or damaged harness--Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. |
| • | Faulty engine coolant temperature (ECT)--Using a scan tool, compare engine coolant temperature with intake air temperature (IAT) on a completely cool engine. The ECT should be within 10°C (50°F) of intake air temperature. If not, replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Determines if the ignition control (IC) module is receiving the CKP sensor 1 signal. If the CKP sensor 1 signal to the ICM is not present, there will be no RPM, spark, or fuel injector pulses.
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Ensures that the IC module has the proper voltage supply and ground.
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Verifies that the IC module is supplying the 10-volt reference to the sensor.
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Check for the proper operation of the CKP sensor 2 signal, IC module and related spark system components. Without the CKP sensor 2 signal the IC module is unable to properly sequence the ignition coils.
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If the CKP sensor 1 signal and CKP sensor 2 signals to the PCM or the medium resolution and low resolution engine speed signals to the IC module short together the vehicle will not start and run. However, there will be spark and fuel injector pulses.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference:
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1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||
2 |
Important: Before proceeding with this diagnostic table, verify that the vehicle's battery is fully charged. Important: If any ignition DTCs are stored as Failed Since Code Clear, diagnose those DTCs before continuing with this diagnosis.
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 3 | ||||||
Does the scan tool indicate an engine RPM? | -- | Go to Step 15 | Go to Step 4 | |||||||
Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 5 | |||||||
5 |
Does the test lamp illuminate? | -- | Go to Step 28 | Go to Step 29 | ||||||
Does the voltage measure near the specified value? | B+ | Go to Step 7 | Go to Step 9 | |||||||
7 | Connect the DMM between the CKP sensor 1 signal terminal and the ground terminal in the connector. Does the voltage measure within the specified range? | 6-8 V | Go to Step 8 | Go to Step 12 | ||||||
8 | Check for faulty terminal connections at the CKP sensor. Repair any connections if necessary. Refer to the following procedures in Wiring Systems: Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 31 | ||||||
9 | Connect the DMM between the CKP 10-volt reference circuit and engine ground. Does the voltage measure near the specified value? | B+ | Go to Step 10 | Go to Step 11 | ||||||
10 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 27 | ||||||
11 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 27 | ||||||
12 |
Does the voltage measure near the specified value? | B+ | Go to Step 13 | Go to Step 14 | ||||||
13 | Locate and repair the short to voltage in the CKP sensor 1 signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 33 | -- | ||||||
14 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 27 | ||||||
Do all of the cylinders have spark? | -- | Go to Step 25 | Go to Step 16 | |||||||
16 | Do any of the cylinders have spark? | -- | Go to Step 21 | Go to Step 17 | ||||||
17 |
Does the voltage measure within the specified range? | 6-8 V | Go to Step 18 | Go to Step 19 | ||||||
18 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 30 | ||||||
19 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 20 | ||||||
20 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 27 | ||||||
21 |
Important:: If carbon tracking is detected on any component, replace that component and the mate.
Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 22 | ||||||
22 |
Did you find and correct the condition? | 5,000-8,000 ohms | Go to Step 33 | Go to Step 23 | ||||||
23 |
Did you find and correct the condition? | 3,000 ohms/ft | Go to Step 33 | Go to Step 24 | ||||||
24 |
Does the test lamp flash continuously while the engine is being cranked? | -- | Go to Step 32 | Go to Step 31 | ||||||
25 |
Are any of the spark plugs fouled? | -- | Go to Engine Compression Test in Engine Mechanical | Go to Step 26 | ||||||
Refer to Diagnostic Aids to check for the following conditions:
Did you find and correct the condition? | -- | Go to Step 33 | Go to Engine Compression Test in Engine Mechanical | |||||||
27 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 31 | ||||||
28 | Locate and repair an open in the ICM ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 33 | -- | ||||||
29 | Locate and repair an open in the ignition 1 voltage circuit to the ICM. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 33 | -- | ||||||
30 | Replace the CKP sensor. Refer to Crankshaft Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 33 | -- | ||||||
31 | Replace the ignition control module. Refer to Ignition Control Module Replacement . Did you complete the replacement? | -- | Go to Step 33 | -- | ||||||
32 | Replace the ignition coils associated with the cylinders that did not have spark. Refer to Ignition Coil Replacement . Did you complete the replacement? | -- | Go to Step 33 | -- | ||||||
33 |
Does the vehicle operate normally, with NO MIL and NO stored DTCs? | -- | System OK | Go to Step 1 | ||||||
