GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Epica 🢒 Engine 🢒 Engine Controls - 2.0L (L34 GMDAT) 🢒 DTC 035

Circuit Description

The electronic control module (ECM) controls the idle speed to a calculated RPM based on inputs and the actual engine RPM. This is determined by the ignition reference pulses received by the ECM from the crankshaft position (CKP) sensor. The ECM uses 4 circuits to move the idle air control (IAC) valve. The IAC valve allows varying amounts of air to flow into the intake manifold, controlling the idle speed.

Conditions for Setting the DTC
    • DTCs 021, 022, and 024 are not set.
    • The throttle is closed.
    • The engine speed is 175 RPM above or below the commanded idle speed for at least 20 seconds.
    • The malfunction indicator lamp (MIL) is not ON.

Diagnostic Aids
    • Inspect for vacuum leaks, unconnected or brittle vacuum hoses, cuts, etc.
    • Inspect the intake manifold and the throttle body gaskets for proper sealing.
    • An IAC valve which does not respond to the ECM, an incorrect base idle adjustment, a damaged throttle body, or damage to the throttle body linkage could create the conditions for setting DTC 035.

Step

Action

Values

Yes

No

1

Was the Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Turn the ignition to LOCK.
  2. Connect the scan tool to the data link connector (DLC).
  3. Monitor the engine RPM.
  4. Disconnect the idle air control (IAC) valve connector.
  5. Connect the IAC driver to the IAC valve.
  6. Start the engine.
  7. Allow the engine to idle in park (P), or neutral (N) for a manual transaxle, with the A/C OFF and the parking brake applied.
  8. Using the IAC driver, extend and retract the IAC valve.

Does the RPM change as the IAC driver is cycled?

--

Go to Step 5

Go to Step 3

3
  1. Turn the ignition to LOCK.
  2. Disconnect the IAC driver from the IAC valve.
  3. Remove the IAC valve from the throttle body.
  4. Inspect the IAC passages for restrictions.

Are the IAC passages restricted?

--

Go to Step 4

Go to Step 14

4
  1. Clean the IAC passages.
  2. Clear any DTCs from the ECM.
  3. Perform the IAC valve reset procedure.
  4. Perform the Diagnostic System Check.

Is the repair complete?

--

System OK

--

5

Cycle the IAC driver while monitoring the engine RPM.

Does the RPM change smoothly within the value specified with each flash of the IAC driver?

700-1,500 RPM

Go to Step 6

Go to Step 3

6
  1. Turn the ignition to LOCK.
  2. Connect the IAC node light to the IAC connector.
  3. Start the engine and cycle the IAC driver.

Do both lights of the IAC node light cycle red and green but never turn OFF as the RPM is changed using the IAC driver?

--

Go to Step 7

Go to Step 9

7
  1. Turn the ignition to LOCK.
  2. Disconnect the IAC driver from the IAC valve.
  3. Measure the resistance between IAC terminals A and B, then C and D.

Is the resistance within the value specified?

40-80 ohms

Go to Step 8

Go to Step 14

8

Measure the resistance between IAC terminals B and C, then A and D.

Does the resistance match the specified value?

∞

Go to Diagnostic Aids

Go to Step 14

9
  1. Turn the ignition to LOCK.
  2. Disconnect the IAC node light from the IAC valve connector.
  3. Inspect for faulty connector terminals.

Is the problem found?

--

Go to Step 13

Go to Step 10

10

Inspect for any open circuits, including connections, between the IAC valve connector terminals and the ECM.

Is the problem found?

--

Go to Step 13

Go to Step 11

11

Inspect for a short to ground between the IAC valve connector terminals and the ECM.

Is the problem found?

--

Go to Step 13

Go to Step 12

12
  1. Turn the ignition ON.
  2. Inspect for a short to voltage between the IAC valve connector terminals and the ECM.

Is the problem found?

--

Go to Step 13

Go to Step 14

13
  1. Turn the ignition to LOCK.
  2. Repair the wire or the connector terminal as needed.
  3. Clear any DTCs from the ECM.
  4. Perform the IAC valve reset procedure.
  5. Perform the Diagnostic System Check.

Is the repair complete?

--

System OK

--

14
  1. Replace the IAC valve. Refer to Idle Air Control Valve Replacement .
  2. Clear any DTCs from the ECM.
  3. Perform the IAC valve reset procedure.
  4. Perform the Diagnostic System Check.

Is the repair complete?

--

System OK

Go to Step 5

15
  1. Replace the ECM. Refer to Engine Control Module Replacement .
  2. Clear any DTCs from the ECM.
  3. Perform the IAC valve reset procedure.
  4. Perform the Diagnostic System Check.

Is the repair complete?

--

System OK

Go to Step 5