DTC P0505 Idle Control System. Geo Prizm 1997

For 1990-2009 cars

Schematic Reference: Refer to Engine Controls Schematics

### Circuit Description

The Powertrain Control Module (PCM) controls engine idle speed with the Idle Air Control (IAC) valve. To increase idle speed, the PCM grounds the OPEN solenoid within the IAC valve. This action opens a plate within the IAC valve, allowing air to bypass the throttle plate. The PCM regulates (fast) idle speed via the IAC valve by increasing the opening of the air bypass port. To decrease idle speed, the PCM grounds the CLOSE solenoid within the IAC valve, thus allowing less air to bypass the throttle plate. The PCM regulates (slow) idle speed via the IAC valve by decreasing the opening of the air bypass port.

When the A/C switch is turned "ON," the A/C amplifier sends the PCM an A/C "ON" signal. In return the PCM will compensate for the extra engine load via the IAC valve, and increase the idle speed. The PCM sends the A/C amplifier an A/C cut-out signal during certain heavy engine loads conditions. When the A/C amplifier receives this signal from the PCM, it will immediately cuts out the A/C compressor operation. When the engine returns to a lighter load the PCM negates the A/C cutout signal. At this point, the A/C amplifier can resume normal cycling of the A/C compressor clutch.

### Conditions for Setting the DTC

Idle speed continues to vary greatly from the target speed.

### Action Taken When the DTC Sets

• | The PCM will illuminate the MIL during the second key cycle in which the DTC sets.

• | The PCM will store the conditions which were present when the DTC set as Freeze Frame Data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn the MIL "OFF" on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.

• | A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault.

• | A DTC can be cleared by using the scan tool "Clear Information" function or by disconnecting the PCM battery feed.

### Diagnostic Aids

An intermittent malfunction may be cause by a poor connection, rubbed through wire insulation, or a broken wire inside the insulation. Inspect harness connectors for backed out terminals, improper matting, broken locks, terminal-to wire connection before component replacement.

With the engine idling, normal operating temperature and all accessories "OFF" monitor the following on the scan tool for correct operation:

• | IAC Duty Cycle - 27-43%

• | Electrical Load - No

• | Commanded A/C - Off

• | Idle Switch - ON

| If any of the above are not functioning properly refer to the applicable circuit.

Check the following conditions:

• | Air intake system for blockage.

• | IAC passage or throttle bore for blockage, excessive deposits in the IAC passage and IAC pintle, and excessive deposits in the throttle bore and throttle blade.

• | Large vacuum leaks.

The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.

If the DTC P0505 does not reset and a driveability symptom still exists, refer to Electrical Load Idle-Up Signal Circuit Check.

### Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

1. The OBD System Check 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. This step checks whether DTC P0505 is the result of a hard failure or an intermittent condition.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the "Powertrain On Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check

2

1. Start the engine and obtain normal operating temperature (Closed Loop).
2. Using a scan tool, monitor the IAC Duty Cycle.

Does the scan tool parameter read within specified range?

27-43%

Go to Step 3

Go to Step 4

3

1. Clear the DTC.
2. Using the scan tool, place the vehicle into Check Mode.
3. Operate vehicle within the "Freeze Frame" conditions as noted.

Does DTC P0500 set?

--

Go to Step 4

Go to Diagnostic Aids

4

1. Turn the ignition switch ON.
2. Using a test light connected to ground, backprobe Idle Air Control (IAC) valve connector cavity 2.

Does test light illuminate?

--

Go to Step 5

Go to Step 11

5

1. Using a DMM, backprobe the PCM connector cavity C3-10.
2. Measure the voltage.

Does DMM read within the specified range?

10-12 V

Go to Step 7

Go to Step 6

6

1. Turn the ignition switch OFF.
2. Disconnect the PCM electrical connector at PCM.
3. Turn the ignition switch ON.
4. Using a DMM, measure voltage at the PCM connector C3-10.

Does DMM read within the specified range?

10-12 V

Go to Step 24

Go to Step 12

7

1. Using a DMM, backprobe the PCM connector cavity C3-9.
2. Measure the voltage.

Does the DMM read the specified value?

0.5 V

Go to Step 9

Go to Step 8

8

1. Turn the ignition switch OFF.
2. Disconnect the PCM electrical connector at PCM.
3. Turn the ignition switch ON.
4. Using a DMM, measure voltage at the PCM connector cavity C3-9.

Does the DMM read the specified value.

12 V

Go to Step 24

Go to Step 13

9

1. Turn the ignition switch OFF.
2. Disconnect the IAC valve electrical connector.
3. Remove the IAC valve.
4. Connect a fused jumper from IAC valve terminal 2 to battery voltage.
5. Connect a fused jumper from IAC valve terminal 3 to ground.

Does IAC valve close?

--

Go to Step 10

Go to Step 22

10

1. Leave fused jumper connected to IAC valve terminal 2.
2. Remove fused jumper from IAC valve terminal 3.
3. Connect a fused jumper from IAC valve terminal 1 to ground.

Does the IAC valve open?

--

Go to Step 14

Go to Step 22

11 | Repair open or short in the power feed circuit between the IAC valve connector and EFI F-HTR. Is the action complete. | -- | Go to Step 25 | --

12

1. Check for an open or short in the IAC valve open control circuit between IAC connector and the PCM.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 25

Go to Step 22

13

1. Check for an open or short in the IAC valve close control circuit between IAC connector and the PCM.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 25

Go to Step 22

14

1. Turn the ignition switch ON.
2. Using a DMM, measure voltage at the PCM connector cavity C1-10.

Does DMM read within specified value?

10 V

Go to Step 17

Go to Step 15

15

1. Turn the ignition switch OFF.
2. Disconnect the PCM connector C1.
3. Using a test light connected to battery voltage, probe PCM cavity C1-10.

Does test light illuminate?

--

Go to Step 16

Go to Step 24

16

1. Check for a short in the A/C "ON" signal circuit between the PCM connector and the A/C amplifier.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 25

Go to Step 23

17

1. Turn the ignition switch ON.
2. Using DMM, backprobe the A/C amplifier connector cavity 3.
3. Measure the voltage.

Does DMM read within the specified range?

10-12 V

Go to Step 20

Go to Step 18

18

1. Using a DMM, backprobe the PCM connector cavity C1-21.
2. Measure the voltage.

Does DMM read within specified voltage?

10 V

Go to Diagnostic Aids

Go to Step 19

19

1. Check for an open or short in the A/C cut-out control circuit between A/C amplifier and PCM connector.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 25

Go to Step 24

20

1. Turn the ignition switch OFF.
2. Disconnect PCM connector C1.
3. Turn the ignition switch ON.
4. Using a DMM, connected from the PCM connector cavity C1-21.

Does DMM read more than specified value?

10 V

Go to Step 22

Go to Step 21

21

1. Check for an open or short in the A/C cut-out control circuit between the A/C amplifier and the PCM connector.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 25

Go to Step 23

22 | Replace the IAC valve. Refer to Idle Air Control Valve Replacement. Is the action complete? | -- | Go to Step 25 | --
23 | Replace the A/C amplifier. Is the action complete? | -- | Go to Step 25 | --
24 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 25 | --
25 | After repairs, use the scan tool clear information function and road test vehicle within "Freeze Frame" conditions that set the DTC. Check for DTC(s). Review scan tool data and if no DTC(s) are stored repair is complete. Are any DTC(s) displayed on scan tool? | -- | Go to the applicable DTC table | System OK