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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1136 (Engine Controls - 3.4L (Troubleshooting & Diagnosis)) >> Troubleshooting >> Crankshaft Position Sensor (CKP) System Diagnosis >> Circuit Description

Circuit Description

WARNING: This page is about a different car, the 2004 Pontiac Aztek and 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

The ignition system uses 2 different types of crankshaft position (CKP) sensors. The ignition control module (ICM) has independent power and ground circuits. The CKP sensor B is used above 1650 RPM. The CKP sensor B provides the ICM with 7X signals. A signal converter within the ICM produces digital 3X pulses to the powertrain control module (PCM). The 3X signal is passed to the PCM on the low resolution engine speed signal circuit. The CKP sensor B is connected directly to the ICM, and consists of the following circuits:

The CKP sensor A connects directly to the PCM, and consists of the following circuits:

The CKP sensor system diagnosis is used to diagnose a fault with CKP sensor B or any of the CKP sensor B circuits.

Crankshaft Position Sensor (CKP) System Diagnosis

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
Connector End View Reference:  Engine Controls Component Views  or  Powertrain Control Module (PCM) Connector End Views 
1 Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2 Attempt to start the engine.
Does the engine start and run?		 - Go to Step 3  Go to Step 4 
3
  1. Turn OFF the ignition.
  2. Disconnect the crankshaft position (CKP) sensor B from the ignition control module (ICM).
  3. Measure the resistance from the CKP sensor signal circuit to the low reference circuit of the CKP sensor B with a DMM. Refer to Circuit Testing in Wiring Systems.
Is the resistance within the specified range?		 800-1,200 Ω Go to Step 4  Go to Step 21 
4
  1. Connect the CKP sensor B.
  2. Disconnect the CKP sensor A.
  3. Observe the 3X crank sensor parameter with a scan tool.
  4. Attempt to crank the engine.
Does the scan tool display a 3X crank sensor RPM ?		 - Go to Intermittent Conditions  Go to Step 5 
5
  1. Turn OFF the ignition.
  2. Connect the CKP sensor A.
  3. Disconnect the ICM.
  4. Turn ON the ignition.
  5. Connect a test lamp between the ICM ignition 1 voltage circuit and a good ground.
Does the test lamp illuminate?		 - Go to Step 6  Go to Step 15 
6 Connect a test lamp between the ignition 1 voltage circuit and the ground circuit of the ICM.
Does the test lamp illuminate?		 - Go to Step 7  Go to Step 16 
7 Test for an intermittent and for a poor connection at the ICM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 23  Go to Step 8 
8
  1. Turn OFF the ignition.
  2. Connect the ICM.
  3. Disconnect the CKP sensor B from the ICM.
  4. Probe the CKP sensor 1 signal circuit of the CKP sensor B with a test lamp connected to battery voltage. Refer to Probing Electrical Connectors in Wiring Systems.
Does the test lamp illuminate?		 - Go to Step 12  Go to Step 9 
9 Probe the CKP sensor 1 signal circuit of the CKP sensor B with a test lamp connected to a good ground. Refer to Probing Electrical Connectors in Wiring Systems.
Does the test lamp illuminate?		 - Go to Step 13  Go to Step 10 
10 Measure the resistance from the CKP sensor signal circuit and the low reference circuit of the CKP sensor B with a DMM. Refer to Circuit Testing in Wiring Systems.
Is the resistance within the specified range?		 800-1,200 mV Go to Step 11  Go to Step 14 
11 Test the CKP sensor B circuits for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 23  Go to Step 22 
12 Test the CKP sensor signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 23  Go to Step 17 
13 Test the CKP sensor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 23  Go to Step 17 
14 Test the CKP sensor B circuits for the following conditions:
  • An open
  • The CKP sensor signal shorted to the low reference

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 23  Go to Step 17 
15
  1. Repair the open or short to ground in the ICM ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.
  2. Replace the fuse if necessary.
Did you complete the repair?		 - Go to Step 23  -
16 Repair the open in the ICM ground circuit. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 23  -
17 Test for an intermittent and for a poor connection at the ICM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 23  Go to Step 18 
18 Test for an intermittent and for a poor connection at the CKP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 23  Go to Step 19 
19
  1. Remove the CKP sensor. Refer to Crankshaft Position (CKP) Sensor Replacement (24X CKP Sensor) or Crankshaft Position (CKP) Sensor Replacement (7X CKP Sensor) .
  2. Visually inspect the CKP sensor for the following conditions:
    • Physical damage
    • Excessive play or looseness
    • Improper installation
    • Foreign material passing between the CKP sensor and the reluctor wheel
    • Excessive air gap between the CKP sensor and the reluctor wheel
    • Electromagnetic interference in the CKP sensor circuits
Did you find and correct the condition?		 - Go to Step 23  Go to Step 20 
20 Inspect the CKP reluctor wheel for the following conditions:
  • Physical damage
  • Excessive end play or looseness
  • Improper installation

Refer to Crankshaft and Bearings Cleaning and Inspection in Engine Mechanical.
Did you find and correct the condition?		 - Go to Step 23  Go to Step 21 
21 Replace the CKP sensor B. Refer to Crankshaft Position (CKP) Sensor Replacement (24X CKP Sensor) or Crankshaft Position (CKP) Sensor Replacement (7X CKP Sensor) .
Did you complete the replacement?		 - Go to Step 23  -
22 Replace the ICM. Refer to Ignition Control Module Replacement .
Did you complete the replacement?		 - Go to Step 23  -
23
  1. Turn the ignition OFF for 30 seconds.
  2. Start the engine and operate the vehicle.
  3. Observe the MIL, vehicle performance, and driveability.
Does the vehicle operate normally, with no MIL?		 - System OK Go to Step 2 
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