Schematic Reference: Engine Controls Schematics
Circuit Description
The Crankshaft Position Sensor is mounted in the engine front cover assembly and works in conjunction with a 4X reluctor wheel on the front of the crankshaft. The CKP sensor has a B+ power supply, a ground and a signal circuit.
As the crankshaft rotates, the reluctor wheel teeth interrupt a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which is read by the PCM. The PCM uses this signal to accurately measure crankshaft velocity which is a variable used to detect misfire. This sensor is not used for spark or fueling. For this diagnostic the PCM monitors the Crankshaft Position Sensor signal, and the Low Resolution and the High Resolution signals from the distributor. During normal operation, at the falling edge of a Crankshaft Sensor signal pulse (signal voltage transitions to low), the PCM starts counting High Resolution pulses. The counter will increase until the PCM detects the leading edge of the next Low Resolution signal pulse (voltage transitions to high). The PCM monitors the number of High Resolution counts to verify proper CKP sensor operation. The scan tool parameter that displays the results of this calculation is CKP:Lo Resolution Angle. The value displayed is the number of degrees that the camshaft deviates [either advanced (+) or retarded (-)] from its normal alignment with the crankshaft. During normal operation, on a vehicle with little or no timing chain wear, the value displayed would be near 0°Dev.
Conditions for Setting the DTC
| • | Engine Speed between 500 and 4000 RPM (LT1), 675 and 4000 RPM (LT4) |
| • | Ignition Voltage between 9 and 17 volts |
| • | CKP:Lo Res Angle goes outside of the range from -10° Dev to +7° Dev but is still within the range -21° Dev to +51° Dev. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails. |
| • | The PCM will record operating conditions at the time the diagnostic fails. The first time the diagnostic fails, this information will be stored in Failure Records. If the diagnostic reports a failure on the second consecutive drive trip, the operating conditions at the time of failure will be written to Freeze Frame and the Failure record will be updated. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail. |
| • | A last test failed (Current DTC) will clear when the diagnostic runs and does not fail. |
| • | A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | PCM battery voltage is interrupted. |
| • | Using a Scan tool. |
Diagnostic Aids
The following mechanical problems may cause this DTC to set:
| • | Poor connections/terminal tension at the sensor. |
| • | Excessive timing chain/gear wear. |
| • | Excessive distributor drive backlash or other mechanical distributor problem. |
| • | Crankshaft reluctor wheel damage or improper installation. |
| • | Engine front cover assembly damage. |
| • | The sensor coming in contact with the reluctor wheel. |
Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame and/or Failure Records data can be useful in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also be used to determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that were noted. This will isolate when the DTC failed.
For intermittents, refer to Symptoms .
Test Description
Number(s) below refer to step numbers on the diagnostic table.
Important: During hard acceleration these two parameters can differ widely from each other due to time variances in the PCMs internal calculating processes. This difference could show up in a snapshot. If other parameters indicate a hard acceleration condition, the difference in the two values should be disregarded.
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If there is excessive timing chain/gear wear, the camshaft has a tendency to retard on acceleration and to advance on deceleration. This parameter will indicate a positive value as the crankshaft accelerates, then flip to a negative value as the crankshaft decelerates. This may be more apparent while driving the vehicle than it is under a no-load situation.
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If the reluctor wheel keyway moves off of the key in the crankshaft before the damper hub is completely installed, it is possible to pinch the reluctor wheel in an incorrect position. This will cause the CKP: Lo Res Angle parameter to be skewed. If the distributor drive pin is not properly indexed into the distributor and then the distributor is drawn into place with the mounting bolts, the CKP: Lo Res Angle parameter will be skewed. Check the condition of the distributor shaft for evidence of this condition.
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The parameter Cyl Mode Misfire Index is the difference in crankshaft deceleration from one reference period to the next (in counts). On a perfect engine this value would equal zero, however, due to normal variations in engine operation, a value less than 1000 is acceptable. In this diagnostic table, Cyl Mode Misfire Index is being used to detect erratic signals from the CKP sensor. The following conditions should be met before using this parameter:
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With the signal generator set to 54 mph, the Crankshaft RPM should indicate approximately 900 RPM.
| • | Engine idling at normal operating temperature. |
| • | All accessories OFF. |
| • | No apparent engine misfire. DTC P0300 may or may not be set since that diagnostic relies on data from this sensor. If the engine is misfiring, this needs to be corrected before proceeding. Refer to Symptoms . |
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||||||
2 | Is DTC P1371 or P1373 also set? | -- | Go to that DTC Table first | |||||||||
Is RPM indicated? | -- | |||||||||||
4 | Using the scan tool, monitor CKP: Lo Res Angle. The actual value may fluctuate, but should remain within the range shown. Is the value within the range specified? | -10° Dev to +7° Dev | ||||||||||
While observing CKP: Lo Res Angle, Quickly rev the engine once and allow it to return to idle. Does the CKP: Lo Res Angle change from a positive value on acceleration to a negative value on deceleration? | -- | |||||||||||
Does the CKP: Lo Res Angle appear to be fixed at or near a value outside the specified range? | - 10° Dev to +7° Dev | |||||||||||
|
Important: Review the information in the Test Description before proceeding. Using the scan tool, monitor Cyl Mode Misfire Index (in the Misfire data list) with the engine idling. Typically this value should remain below 1000. Is the value below the specified value? | 1000 | |||||||||||
8 |
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Diagnostic Aids | |||||||||
9 |
Is the test light ON? | -- | ||||||||||
10 | Connect a test light (J 34142-B) from the ignition feed circuit to the ground circuit in the Crankshaft Position Sensor harness connector. Is the test light ON? | -- | ||||||||||
Does the scan tool indicate Crankshaft RPM? | -- | |||||||||||
12 | Visually inspect the Crankshaft Position Sensor for the following conditions:
Was a problem found and corrected? | -- | ||||||||||
13 |
Does the DVM display the value shown (or lower)? | 5 ohms | ||||||||||
14 | Check for excessive timing chain/gear wear. Refer to Engine Unit Repair, Section 6A. Is the action complete? | -- | -- | |||||||||
15 | Check for poor connections/terminal tension at the sensor. If the connections are OK, Check for proper reluctor wheel installation. Refer to Engine Unit Repair, Section 6A. Is the action complete? | -- | -- | |||||||||
16 | Check for poor connections/terminal tension at the sensor. Was a problem found and corrected? | -- | ||||||||||
17 | Repair the ignition feed circuit Is the action complete? | -- | -- | |||||||||
18 | Repair the ground circuit Is the action complete? | -- | -- | |||||||||
19 | Repair the signal circuit Is the action complete? | -- | -- | |||||||||
20 | Replace the Crankshaft Position Sensor. Is the action complete? | -- | -- | |||||||||
21 |
Important:: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | -- | |||||||||
22 |
Does the scan tool indicate that this test ran and passed? | -- | ||||||||||
23 | Using the scan tool, select Capture Info, Review Info. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
