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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1350 (Engine Control System (Troubleshooting & Diagnosis) -- 1.8L (LNK)) >> Troubleshooting >> Electrical/Accessory Load Idle-Up Signal Diagnosis >> Test Description

Test Description

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

The numbers below refer to the step numbers in the diagnostic table.

  1. 1:  The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
  2. 2:  This step verifies whether the PCM responds to the operation of the rear defogger. The IAC Motor Command Cycle percentage and the idle speed will increase when the rear defogger is turned ON if the idle-up system is OK.
  3. 3:  This step verifies whether the PCM responds to the operation of the taillights. The IAC Motor Command Cycle percentage and the idle speed will increase when the taillights are turned ON if the idle-up system is OK.
  4. 4:  This step verifies the operation of the A/C idle circuit. If the engine idle speed and IAC Motor Command cycle increase when the A/C is turned ON, the A/C idle circuit is functioning normally.
  5. 5:  This step verifies the operation of the power steering pressure (PSP) switch circuit. If the engine idle speed and IAC Motor Command increase when the steering wheel is turned to 90 percent, the PSP switch idle circuit is functioning normally.
  6. 6:  This step tests the PSP switch signal circuit for voltage from the PCM.
  7. 7:  This step tests the operation of the PSP switch.
  8. 10:  The A/C compressor clutch should not be engaged with the A/C switch Off. The PCM will not increase engine idle speed when the A/C compressor is supposed to be Off.
  9. 13:  If the A/C compressor clutch engages, the compressor clutch, the relay, and the control circuit are all OK. The PCM will then need to be replaced because there was no increase in the IAC motor command percentage during A/C operation in Step 4.
  10. 22:  This step tests for a short to ground in the Diagnostic Request circuit. A short to ground in the Diagnostic Request circuit can cause the PCM to ignore the idle-up signals to the PCM. A short in the Diagnostic Request circuit will cause the IAC Motor Command and the idle speed to remain fixed.
Electrical/Accessory Load Idle-Up Signal Diagnosis

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
1  Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2 
IMPORTANT: Check that the rear defogger and the parking lamps operate correctly before using this table.
  1. Install a scan tool.
  2. Start the engine.
  3. Run vehicle at idle with the accessories OFF, until normal operating temperature is reached.
  4. Monitor the IAC Motor Command parameter on the scan tool while turning the rear defogger switch ON and OFF.
Does the scan tool indicate that the IAC Motor Command increased the specified amount when the rear defogger switch was turned ON?		 1-3% Go to Step 3  Go to Step 18 
3  Monitor the IAC Motor Command parameter on the scan tool while turning the parking lamp switch ON and OFF.
Does the scan tool indicate that the IAC Motor Command increased the specified amount when the parking lamp switch was turned ON?		 1-3% Go to Step 4  Go to Step 20 
4 
  1. Monitor the IAC Motor Command parameter on the scan tool.
  2. Turn the A/C switch ON and the blower speed selector switch to any position except OFF.
Does the IAC Motor Command increase within the specified range when the A/C is turned ON?		 4-14% Go to Step 5  Go to Step 10 
5 
  1. Monitor the IAC Motor Command parameter on the scan tool.
  2. Turn the steering wheel to the right and to the left.
  3. Return the steering wheel to the center, straight ahead position.
Did the scan tool indicate that the IAC Motor Command increased the specified amount when the steering wheel was turned all the way in either direction?		 2-10% System OK Go to Step 6 
6 
  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the PSP switch electrical connector.
  3. Measure the voltage from the PSP switch connector to ground on the harness side with a DMM.
Is the voltage near the specified value?		 B+ Go to Step 7  Go to Step 8 
7 
  1. Connect a test lamp to B+.
  2. Probe the PSP switch connector on the switch side with the test lamp.
  3. Start the engine.
  4. Observe the test lamp while turning the steering wheel to the right and to the left.
Does the test lamp illuminate when the steering wheel is turned to the right and to the left?		 - Go to Step 22  Go to Step 9 
8
  1. Check for an open or a short to ground in the PSP switch signal circuit between the PCM and the PSP switch.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Did you find and correct a condition?		 - Go to Step 25  Go to Step 24 
9
  1. Check for a faulty ground connection at the power steering pump.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Did you find and correct a condition?		 - Go to Step 25  Go to Step 23 
10 
  1. Start the engine.
  2. Turn ON the HVAC blower switch to any speed.
  3. Turn the A/C switch OFF.
Is the A/C compressor clutch engaged?		 - Go to Step 14  Go to Step 11 
11
  1. Continue to run the engine with HVAC blower ON and the A/C OFF.
  2. Backprobe the A/C Clutch Relay Control circuit at the PCM connector with a DMM connected to ground.
  3. Measure the voltage.
Does the voltage equal the specified value?		 B+ Go to Step 12  Go to Step 17 
12
  1. Turn ON the A/C.
  2. Backprobe the A/C Clutch Relay Control circuit at the PCM connector with a DMM connected to ground.
  3. Measure the voltage.
Did the voltage drop to within the specified value when the A/C was turned ON?		 0.0-1.0 V Go to Step 13  Go to Step 24 
13  Did the A/C compressor engage when the A/C was turned ON? - Go to Step 24  Go to Step 16 
14
  1. Test for a short to ground in the A/C Clutch Relay Control circuit between the PCM and the A/C compressor clutch relay.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Did you find and correct a condition?		 B+ Go to Step 25  Go to Step 15 
15
  1. Turn OFF the ignition.
  2. Disconnect the PCM C3 connector.
  3. Start the engine.
  4. Turn ON the HVAC blower switch to any speed.
Is the A/C compressor engaged?		 - Go to Compressor Relay Replacement in Heating, Ventilation, and Air Conditioning Go to Step 24  PCM
16
  1. There is a fault in an HVAC electrical circuit or component.
  2. Inspect and repair as necessary. Refer to Air Conditioning (A/C) System Performance Test in Heating, Ventilation, and Air Conditioning.
Did you complete the repair?		 - Go to Step 25  -
17
  1. There is no ignition positive voltage at the A/C Clutch Relay Control circuit. Inspect for any of the following conditions:
    • Test for an open in the A/C Clutch Relay Control circuit between the PCM and the A/C compressor clutch relay.
    • Test for a faulty A/C compressor clutch relay or repair the cause of no ignition positive voltage to the relay. Refer to Air Conditioning (A/C) System Performance Test in Heating, Ventilation, and Air Conditioning.
  2. Repair as necessary.
Did you complete the repair?		 - Go to Step 25  -
18
  1. Turn ON the ignition, with the engine OFF.
  2. Backprobe the Electrical Load Idle-Up Signal Defogger circuit at the PCM connector with a test lamp connected to ground.
  3. Turn ON the rear defogger switch.
Does the test lamp illuminate?		 - Go to Step 22  Go to Step 19 
19
  1. Turn OFF the ignition.
  2. Test the Electrical Load Idle-Up Signal Defogger circuit for an open or a short.
  3. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Did you find and correct a condition?		 - Go to Step 25  Go to Diagnostic Starting Point - Stationary Windows in Stationary Windows
20
  1. Turn ON the ignition, with the engine OFF.
  2. Backprobe the Electrical Load Idle-Up Signal Taillights circuit at the PCM connector with a test lamp connected to ground.
  3. Turn ON the parking lamp switch.
Does the test lamp illuminate?		 - Go to Step 22  Go to Step 21 
21
  1. Turn OFF the ignition.
  2. Test the Electrical Load Idle-Up Signal Taillights circuit for an open or a short.
  3. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Did you find and correct a condition?		 - Go to Step 25  Go to Diagnostic Starting Point - Lighting Systems in Lighting Systems
22 
  1. Test for a short to ground in the Diagnostic Request circuit from the PCM and the data link connector (DLC).
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Did you find and correct a condition?		 - Go to Step 25  Go to Step 24 
23 Replace the PSP switch. Refer to Power Steering Pressure Switch Replacement in Power Steering Systems.
Did you complete the replacement?		 - Go to Step 25  -
24 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .
Did you complete the replacement?		 - Go to Step 25  -
25 Operate the vehicle within the conditions that the concern was first noticed.
Does the system now operate properly?		 - System OK Go to Diagnostic Aids
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