The idle speed control (ISC) assembly is a throttle body with an integrated motor that is used to control the engine speed at idle. The engine control module (ECM) commands the integrated ISC motor to adjust the throttle angle for idle speed control. The ECM uses a high control circuit and a low control circuit to command the ISC motor. If the ECM detects that the actual ISC motor position can not be commanded to the desired position, this DTC sets.
This diagnostic procedure supports the following DTC:
DTC P1512 Idle Speed Control (ISC) System
• | DTCs P0222 and P0223 are not set. |
• | The engine is running. |
• | The ignition 1 voltage is more than 10 volts. |
• | The ISC motor angle is between 0.2-5.6 degrees. |
• | This DTC runs continuously once the above conditions are met. |
The ECM detects that the actual ISC motor position can not be controlled to the desired ISC motor position for more than 5 seconds.
• | The malfunction indicator lamp (MIL) will illuminate after 3 consecutive trips with a fail. |
• | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
The malfunction indicator lamp (MIL) will illuminate.
• | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
• | DTCs can be cleared by using the scan tool. |
• | Disconnect the ECM battery feed for more than 10 seconds. |
• | The MIL will turn OFF after the diagnostic runs without a fault. |
• | DTCs can be cleared by using the scan tool. |
• | Disconnect the ECM battery feed for more than 10 seconds. |
The numbers below refer to the step numbers on the diagnostic table.
This step tests for a high resistance on the ISC motor position sensor 5-volt reference circuit.
This step tests for a high resistance on the ISC motor high control circuit.
This step tests for a high resistance on the ISC motor low control circuit.
Step | Action | Values | Yes | No | ||||||||||||||||||
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Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||||||||||||
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | |||||||||||||||||||
2 |
Is DTC P0122, P0123, P0222, P0223, or P1511 also set? | -- | Go to Step 3 | |||||||||||||||||||
3 |
Does the idle speed control (ISC) motor position sensor parameter change when the throttle is open? | -- | Go to Step 4 | Go to Step 5 | ||||||||||||||||||
4 |
Does the DTC fail this ignition cycle? | -- | Go to Step 5 | Go to Intermittent Conditions | ||||||||||||||||||
5 |
Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 6 | ||||||||||||||||||
Notice: Do NOT use the low reference circuit in the component harness connector for this test. Damage to the control module may occur due to excessive current draw. Important: Use a test lamp that measures more than 20 ohms for this test. Is the voltage more than the specified value? | 4.8 V | Go to Step 7 | Go to Step 9 | |||||||||||||||||||
Is the voltage more than the specified value? | 0.3 V | Go to Step 8 | Go to Step 10 | |||||||||||||||||||
Is the voltage more than the specified value? | 0.3 V | Go to Step 12 | Go to Step 11 | |||||||||||||||||||
9 | Test the 5-volt reference circuit of the ISC motor position sensor for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14 | ||||||||||||||||||
10 | Test the high control circuit of the ISC motor for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14 | ||||||||||||||||||
11 | Test the low control circuit of the ISC motor for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14 | ||||||||||||||||||
12 | Test the signal circuit of the ISC motor position sensor for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 13 | ||||||||||||||||||
13 | Test for an intermittent and for a poor connection at the throttle body assembly. 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 17 | Go to Step 15 | ||||||||||||||||||
14 | Test for an intermittent and for a poor connection at the engine control module (ECM). 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 17 | Go to Step 16 | ||||||||||||||||||
15 | Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||||||||
16 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||||||||
17 |
Does the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 18 | ||||||||||||||||||
18 | Are there any DTCs that have not been diagnosed? | -- | System OK |