Diagnostic Instructions

DTC Descriptors

DTC P1511: Idle Speed Control (ISC) Motor Control Circuit

DTC P1512: Idle Speed Control (ISC) System

DTC P1513: Idle Speed Control (ISC) System Performance

Diagnostic Fault Information

Circuit	Short to Ground	High Resistance	Open	Short to Voltage	Signal Performance
5-Volt Reference	P0122, P0222	P0510, P2119, P1513	P0122, P0222	P0123, P0223	--
Idle Motor Position Signal	P0222	P1512	P0222	P0223	--
Idle Motor Switch Signal	P0510	--	P0510	--	--
Throttle Position Sensor Signal	P0122	P0510	P0122	P0123	--
Idle Motor High Control	P1511, P1512	P1511, P1512	P1511, P1512	P1511, P1512	--
Idle Motor Low Control	P1511, P1512	P1511, P1512	P1511, P1512	--	--
Low Reference	--	--	P0123, P0223	--	--

Typical Scan Tool Data

ISC Command

Circuit	Short to Ground	Open	Short to Voltage
Operating Conditions: Engine operating in closed loop Parameter Normal Range: ISC Command 30%
Idle Motor High Control	-40%	0%	0%
Idle Motor Low Control	0%	0%	-40%

Circuit/System Description

The throttle body assembly uses an idle speed control (ISC) system that contains motor, throttle position (TP) sensor, motor position sensor, and an idle switch. The ISC system is used to control engine speed at idle. The engine control module (ECM) uses high and low control circuits to control the ISC motor. A 5-volt reference and low reference supplied by the ECM is shared by both the TP and motor position sensors. The TP and motor position sensors each have a signal circuit to feedback voltage to the ECM. The ECM commands the ISC motor by pulse width modulating the voltage on the high and low control circuits to adjust the throttle angle for idle speed control. The motor position sensor is used by the ECM to monitor the position of the ISC motor for idle operation. The TP sensor is used by the ECM to monitor the position of the throttle blade. An idle switch is used by the ECM to monitor when the throttle blade is at it rest position to allow the ISC motor to control idle operation. With the throttle blade at the rest position, the idle switch will be closed. When the throttle blade is opened, the idle switch will be open.

The ISC system consist of the following circuits:

Conditions for Running the DTC

P1511

P1512

P1513

Conditions for Setting the DTC

P1511

The ECM has commanded a duty cycle of the ISC motor more than 25 percent or less than -42 percent for 6 seconds.

P1512

The ECM can not command the ISC motor to the desired position for 5 seconds.

P1513

The ECM detects the adaptation value exceeds the TP sensor or the ISC position sensor values.

Action Taken When the DTC Sets

DTC P1511 and P1512 are Type B DTCs. DTC P1513 is a Type C DTC.

Conditions for Clearing the DTC

DTC P1511 and P1512 are Type B DTCs. DTC P1513 is a Type C DTC.

Reference Information

Schematic Reference

Engine Controls Schematics

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Ignition ON, command the ISC motor ON with a scan tool. The reading should fluctuate between 3-5 percent.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Verify the following conditions do not exist:

•	The throttle body is not damaged or modified.

•	Vacuum leaks

•	A restricted air intake system

•	Excessive deposits on the throttle plate or bore

•	The throttle shaft for binding

•	The throttle linkage or the throttle cable for binding

•	Incorrectly installed positive crankcase ventilation (PCV) valve or hose

•	A malfunctioning PCV valve

⇒	If you find any of the above conditions, repair as necessary.

2. Ignition OFF, disconnect the harness connector at the ISC motor.
3. Ignition On, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 2 and ground.

⇒	If less than the specified range, test the 5-volt reference circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the ECM.

4. Test for less than 0.3 volt between the high control circuit terminal 1 and 12 volts.

⇒	If greater than the specified range, test the high control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

Important: Use the AC volt scale on the DMM. The millivolt scale will produce an inaccurate reading.

5. Engine running, test for 30-40 hertz on the AC scale between the high control circuit terminal 1 and ground.

⇒	If not within the specified range, test the high control circuit for a short to voltage. If the circuit tests normal, replace the ECM.

6. Ignition OFF, verify that a test lamp does not illuminate between the low control circuit terminal 5 and 12 volts.

⇒	If test lamp illuminates, test the low control circuit for a short to ground. If the circuit tests normal, replace the ECM.

7. Ignition ON, test for less than 0.3 volt between the low control circuit terminal 5 and ground.

⇒	If greater than the specified range, test the low control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

8. If all circuits test normal, test or replace the ISC motor.

Component Testing

1. Ignition OFF, disconnect the harness connector at the ISC motor.
2. Test for 3-6 ohms of resistance between the high control terminal 1 and the low control terminal 5.

⇒	If not within the specified range, replace the ISC motor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.