Step
Action
Values
Yes
No
Schematic Reference: Engine Controls Schematics
1
Did you perform the Diagnostic System Check-Engine Controls?
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Go to
Step 2
Go to
Diagnostic System Check - Engine Controls
2
Important: If DTC P1120, P1220, P1221, P1515 or P1516 are set, refer to the appropriate DTC first for further diagnosis.
Operate the vehicle within Failure Records conditions.
Does the scan tool indicate DTC P1518 failed this ignition?
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Go to
Step 3
Go to Diagnostic Aids
3
- <LI type=1>Turn OFF the ignition. <LI type=1>Disconnect the TAC module.
- With the ignition OFF, measure the voltage of the TAC module ignition feed circuit using a DMM that is connected to a good ground.
Is voltage at or near the specified value?
0 V
Go to
Step 4
Go to
Step 10
4
- <LI type=1>Turn ON the ignition, with the engine OFF.
- Measure the voltage from the TAC module ignition feed circuit using a DMM that is connected to a good ground.
Does the voltage measure at or near the specified value?
B+
Go to
Step 5
Go to
Step 12
5
Test the TAC module ground circuits using a test lamp that is connected to B+.
Does the test lamp illuminate when probing both circuits?
--
Go to
Step 6
Go to
Step 13
6
Test for voltage between both TAC module serial data circuits and a good ground using a DMM.
Does the voltage measure within the specified values?
2-5 V
Go to
Step 14
Go to
Step 7
7
Does the voltage measure more than the specified value?
5 V
Go to
Step 11
Go to
Step 8
8
Does the voltage measure less than the specified value?
5 V
Go to
Step 9
--
9
Test for an open or short to ground in the serial data circuit. Refer to
Circuit Testing and
Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
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Go to
Step 18
Go to
Step 16
10
Repair the short to battery voltage in the ignition feed circuit. Refer to
Wiring Repairs in Wiring Systems.
Did you complete the repair?
--
Go to
Step 18
--
11
Test for a short to voltage on the TAC module serial data circuit. Refer to
Circuit Testing and
Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to
Step 18
Go to
Step 17
12
Repair the open or short to ground in the ignition feed circuit. Refer to
Wiring Repairs in Wiring Systems.
Did you complete the repair?
--
Go to
Step 18
--
13
Repair the open in the TAC module ground circuit. Refer to
Wiring Repairs in Wiring Systems.
Did you complete the repair?
--
Go to
Step 18
--
14
Inspect for a faulty serial data connections at the TAC module. Refer to
Testing for Intermittent Conditions and Poor Connections and
Connector Repairs in Wiring Systems.
Did you find and correct the condition?
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Go to
Step 18
Go to
Step 15
15
Replace the TAC module. Refer to
Accelerator Pedal Position Sensor Replacement .
Did you complete the replacement?
--
Go to
Step 18
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16
Inspect for faulty connections at the PCM. 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 18
Go to
Step 17
17
Replace the PCM. Refer to
Powertrain Control Module Replacement .
Did you complete the replacement?
--
Go to
Step 18
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18
- <LI type=1>Use the scan tool in order to clear the DTCs. <LI type=1>Turn OFF the ignition for 30 seconds.
- Operate the vehicle within the Conditions For Running the DTC as specified in the supporting text.
Does the DTC run, and pass?
--
Go to
Step 19
Go to
Step 2
19
With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?
--
Go to
Diagnostic Trouble Code (DTC) List
System OK
P1518
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 monitors the accuracy of the serial data transmitted between the TAC module and the PCM. If the PCM of the TAC module detects a loss of data or invalid data, this DTC sets.
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Conditions for Running the DTC
The ignition switch is in the crank or run position.
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Conditions for Setting the DTC
Invalid or missing serial data messages are detected for a predetermined period of time.
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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/Failure Records.
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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.
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Diagnostic Aids
Inspect for the following:
Important: DTC P1518 sets if the battery voltage is low or the PCM is replaced or reflashed. If the customer's concern is slow cranking, or if the engine is not cranking because the battery voltage is low, ignore DTC P1518. Clear any DTCs from memory that may have set from the low battery voltage condition.
If the condition is intermittent, refer to
Intermittent Conditions .
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Test Description
The number below refers to the step number on the diagnostic table.
- When the PCM detects a condition within the electronic throttle control (ETC) system other DTCs may set due to the many redundant tests run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Keep this in mind when reviewing captured DTC info.
