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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 3684
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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How to fix 2003 chevy silverado P1518?

Customer Question

How to fix 2003 chevy silverado P1518?
Submitted: 4 years ago.
Category: Chevy
Expert:  Jerry Newton replied 4 years ago.

CIRCUIT DESCRIPTION
The throttle actuator control (TAC) module and the powertrain control module (PCM) communicate via a dedicated serial data circuit. This serial data circuit is separate from any other serial data circuit on the vehicle. Accurate transmitting and receiving of serial data requires not only good circuit integrity but also adequate system voltage. This diagnostic test monitors the accuracy of the serial data transmitted between the TAC module and the PCM. If the PCM detects a loss of data or invalid data, this DTC sets.

CONDITIONS FOR RUNNING THE DTC

  • The ignition switch is in the crank or run position.
  • The ignition voltage is more than 5.23 volts .

CONDITIONS FOR SETTING THE DTC

  • Invalid or missing serial data messages are detected for a predetermined amount of time.
  • The above condition is met for more than 1 second .

ACTION TAKEN WHEN THE DTC SETS

  • The PCM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
  • The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or the Failure Records.
  • The PCM commands the TAC system to operate in the Reduced Engine Power mode.

OR

  • Under certain conditions the PCM commands the engine OFF.
  • The message center displays Reduced Engine Power.

CONDITIONS FOR CLEARING THE MIL/DTC

  • The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
  • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
  • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
  • Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS

  • DTC P1518 sets if the battery voltage is low. If the customer's concern is slow cranking or no crank because battery voltage is low, ignore DTC P1518. Clear any DTCs from memory that may have set from the low battery voltage condition.
  • DTC P1518 sets when there is a short to B+ on the TAC module ground circuit. Inspect the fuses for the circuits that are in the TAC module harness-i.e. cruise, brake. An inspection of the fuses may lead you to the circuit that is shorted to the TAC module ground circuit.
  • DTC P1518 sets if the TAC module ignition feed circuit is shorted to a B+ supply circuit. The TAC module stays powered-up when the ignition switch is turned OFF. When the ignition switch is turned ON, the TAC module is powered-up before the PCM. DTC P1518 sets because no communication is detected by the TAC module from the PCM. Inspect related circuits for being shorted to a B+ supply circuit.
  • Inspect the TAC module power and ground circuits and the TAC module/PCM serial data circuits for intermittent connections.
  • Inspect the TAC module connectors for signs of water intrusion. If water intrusion occurs, multiple DTCs may set without any circuit or component conditions found during diagnostic testing.
  • When the TAC module detects a problem within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing an individual condition may correct more than 1 DTC. Remember this if you review the stored information in Capture Info.
  • For an intermittent condition, refer to Intermittent Conditions. See: Initial Inspection and Diagnostic Overview\Diagnostic Strategies\Intermittent Conditions

TEST DESCRIPTION

Steps 1-4

Steps 5-7

Steps 8-10

Steps 11-13

Steps 14-18

Steps 19-22

Steps 23-29

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

  1. This step determines if the ignition relay is supplying a voltage to the ETC fuse.
  1. Increasing the engine speed to 3,000 RPM aids in locating a shorted throttle actuator motor control circuit. Depending on the polarity of the throttle actuator motor transistors, this DTC may not set with a fault in the control circuits. The throttle actuator motor is a bi-directional DC motor. Raising the engine speed changes the polarity of the transistors in the throttle actuator motor. This occurs because 1 set of the transistors are low, 0 volts , and the other set are high, B+. Therefore, if 1 set of transistors are at a low voltage and the corresponding circuit is shorted low, DTC P1518 will not set. When the polarity of the transistors change, this DTC sets. If this DTC does not fail this ignition, continue to monitor this DTC status while moving related harnesses and connectors.
  1. Locating and repairing an individual condition may correct more than 1 DTC.




Having said all of that, it is most commonly due to a faulty throttle body.
Customer: replied 4 years ago.
I can not open TEST DESCRIPTION file. I need to know How to check? step by step
Expert:  Jerry Newton replied 4 years ago.
I'm sorry, the formatting didn't come out right on that. I'm working with a new computer and browser, and still working out some of the bugs. Let me try again.

Circuit Description

The throttle actuator control (TAC) module and the powertrain control module (PCM) communicate via a dedicated serial data circuit. This serial data circuit is separate from any other serial data circuit on the vehicle. Accurate transmitting and receiving of serial data requires not only good circuit integrity but also adequate system voltage. This diagnostic test monitors the accuracy of the serial data transmitted between the TAC module and the PCM. If the PCM detects a loss of data or invalid data, this DTC sets.

Conditions for Running the DTC

The ignition switch is in the crank or run position.
The ignition voltage is more than 5.23 volts.

Conditions for Setting the DTC

Invalid or missing serial data messages are detected for a predetermined amount of time.
The above condition is met for more than 1 second.

Action Taken When the DTC Sets

The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
The control module commands the TAC system to operate in the Reduced Engine Power mode.
A message center or an indicator displays Reduced Engine Power.
Under certain conditions the control module commands the engine OFF.

Conditions for Clearing the MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

Important: Reprogramming the PCM may cause a communication error between the PCM and the TAC. If the PCM detects a communication error, DTC P1518 sets. Clear any DTCs from the memory that may have been set by Reprogramming.

DTC P1518 sets if the battery voltage is low. If the customer's concern is slow cranking or no crank because battery voltage is low, ignore DTC P1518. Clear any DTCs from memory that may have set from the low battery voltage condition.
DTC P1518 sets when there is a short to B+ on the TAC module ground circuit. Inspect the fuses for the circuits that are in the TAC module harness--i.e. cruise, brake. An inspection of the fuses may lead you to the circuit that is shorted to the TAC module ground circuit.
DTC P1518 sets if the TAC module ignition feed circuit is shorted to a B+ supply circuit. The TAC module stays powered-up when the ignition switch is turned OFF. When the ignition switch is turned ON, the TAC module is powered-up before the PCM. DTC P1518 sets because no communication is detected by the TAC module from the PCM. Inspect related circuits for being shorted to a B+ supply circuit.
Inspect the TAC module power and ground circuits and the TAC module/PCM serial data circuits for intermittent connections.
Inspect the TAC module connectors for signs of water intrusion. If water intrusion occurs, multiple DTCs may set without any circuit or component conditions found during diagnostic testing.
When the TAC module detects a problem within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing an individual condition may correct more than 1 DTC. Remember this if you review the stored information in Capture Info.
For an intermittent condition, refer to Intermittent Conditions .

Test Description

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

  1. This step determines if the ignition relay is supplying a voltage to the ETC/ECM fuse.

  2. Increasing the engine speed to 3,000 RPM aids in locating a shorted throttle actuator motor control circuit. Depending on the polarity of the throttle actuator motor transistors, this DTC may not set with a fault in the control circuits. The throttle actuator motor is a bi-directional DC motor. Raising the engine speed changes the polarity of the transistors in the throttle actuator motor. This occurs because 1 set of the transistors are low, 0 volts, and the other set are high, B+. Therefore, if 1 set of transistors are at a low voltage and the corresponding circuit is shorted low, DTC P1518 will not set. When the polarity of the transistors change, this DTC sets. If this DTC does not fail this ignition, continue to monitor this DTC status while moving related harnesses and connectors.

  3. Locating and repairing an individual condition may correct more than 1 DTC.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Turn ON the ignition, with the engine OFF.
  2. Remove the cover from the underhood electrical center.
  3. Test both sides of the ETC/ECM fuse with a test lamp connected to ground.

Does the test lamp illuminate on at least 1 side of the fuse?

--

Go to Step 3

Go to Ignition Relay Diagnosis

3

  1. Turn OFF the ignition
  2. Test for voltage at the ETC/ECM fuse with a test lamp connected to ground.

Does the test lamp illuminate?

--

Go to Step 22

Go to Step 4

4

Connect a scan tool.

Is DTC P0604 also set?

--

Go to DTC P0601, P0602, P0603, P0604, P0605, P0606, P0607, P1600, P1621, P1627, P1680, P1681, P1683, or P2610

Go to Step 5

5

Important: If the Driver Information Center is displaying Reduced Engine Power, go to step 6.

  1. Start the engine.
  2. Increase the engine speed to 3000 RPM, if possible.
  3. Monitor the diagnostic trouble code (DTC) Info option using the scan tool.

Does the scan tool indicate this DTC failed this ignition?

--

Go to Step 6

Go to Diagnostic Aids

6

  1. Turn OFF the ignition.
  2. Disconnect the throttle actuator motor harness connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Test for voltage at both throttle actuator motor control circuits with a DMM.

Does the DMM indicate voltage on both circuits above the specified value?

1 V

Go to Step 12

Go to Step 7

7

  1. Turn OFF the ignition.
  2. Disconnect the throttle actuator control (TAC) module connectors.
  3. Test both throttle actuator motor control circuits for continuity to ground with a DMM.

Does the DMM indicate continuity to ground?

--

Go to Step 10

Go to Step 8

8

  1. Turn OFF the ignition.
  2. Remove the ETC/ECM fuse.
  3. Test the TAC side of the fuse terminal for continuity to ground with a DMM.

Does the DMM indicate continuity to ground?

--

Go to Step 9

Go to Step 11

9

  1. Disconnect the TAC module 16-way harness connector.
  2. Test the TAC side of the fuse terminal for a short to ground with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 24

10

  1. Disconnect the TAC module 16-way harness connector.
  2. Test the throttle actuator motor control circuits for a short to ground at the TAC module 16-way harness connector with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 24

11

  1. Turn OFF the ignition.
  2. Disconnect the TAC module 16-way harness connector.
  3. Test the TAC module ignition feed circuit for an open or high resistance with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 24

12

  1. Turn OFF the ignition.
  2. Disconnect the TAC module 16-way connector.
  3. Turn ON the ignition, with the engine OFF
  4. Test for a short to voltage at both throttle actuator motor control circuits with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 13

13

  1. Turn OFF the ignition
  2. Disconnect the TAC module 10-way harness connector.
  3. Test for a short between each throttle actuator motor control circuit and all other TAC module circuits with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 14

14

Test for an open or high resistance in the TAC module ground circuit with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 15

15

Test for voltage on the serial data circuits at the TAC module 16-way harness connector with a DMM.

Does the DMM indicate voltage within the specified values for both circuits?

0-4.5 V

Go to Step 16

Go to Step 18

16

  1. Turn OFF the ignition.
  2. Test both serial data circuits at the TAC module 16-way harness connector for continuity to ground with a DMM.

Does the DMM indicate OL for both circuits?

--

Go to Step 20

Go to Step 17

17

  1. Disconnect the powertrain control module (PCM) connector containing the TAC module serial data circuits.
  2. Test both serial data circuits at the TAC module 16-way connector for a short to ground with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 18

18

Test for a short between both serial data circuits and all other circuits at the PCM and TAC module harness connectors with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 19

19

Test for a short to voltage on both serial data circuits at the TAC module 16-way connector with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 25

20

  1. Disconnect the PCM connector that contains the TAC module serial data circuits.
  2. Test each serial data circuit between the TAC module 16-way harness connector and the PCM harness connector for an open or high resistance with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 21

21

  1. Connect the PCM.
  2. Turn ON the ignition.
  3. Test for voltage on the serial data circuit at the TAC module 16-way harness connector with a DMM.

Does the DMM indicate voltage at the specified value?

0 V

Go to Step 25

Go to Step 24

22

  1. Turn OFF the ignition
  2. Disconnect the 16-way TAC module harness connector.
  3. Test the TAC module ignition feed circuit for a short to battery voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 23

23

  1. Turn ON the ignition.
  2. Test both TAC motor circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 24

24

Test for poor connections at the TAC module harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 26

25

Test for poor connections at the PCM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 27

26

Replace the TAC module. Refer to Electronic Throttle Actuator Control Module Replacement .

Did you complete the replacement?

--

Go to Step 28

--

27

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 28

--

28

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 29

29

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK

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