| Table 1: | DTC P1518 - PCM to TAC Module Serial Data Circuit |
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 detects a loss of data or invalid data, this diagnostic trouble code (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. |
| • | All of the above conditions are met for less than 1 second. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) when this diagnostic runs and fails. |
| • | The Reduced Engine Power message displays on the drivers information center. |
| • | The PCM records the operating conditions at the time during which the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records. |
| • | If no other TAC system DTCs are set, the TAC system will operate in Reduced Engine Power mode. If certain TAC system DTCs are set at the same time, the TAC system either defaults to a more tightly restricted mode of operation if the TAC determines that limited safe operation is possible, or the TAC commands the engine to shut down. |
| • | If DTC P0606 is set with DTC P1518, the TAC commands an engine shut down. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL after three consecutive drive trips during which the diagnostic runs and does not fail. |
| • | A last test failed current DTC will clear when the diagnostic runs and does not fail. |
| • | A History DTC clears after forty consecutive warm-up cycles if this or any other emission related diagnostic does not report any failures. |
| • | Clear the MIL/DTC information with a scan tool. |
Diagnostic Aids
Important:
• Remove any debris from the PCM or TAC module connector surfaces before
servicing the PCM or TAC module. Inspect the PCM or TAC module connector gaskets
when diagnosing/replacing the modules. Ensure that the gaskets are installed
correctly. The gaskets prevent contaminate intrusion into the PCM or TAC
modules. • For any test that requires probing the PCM or a component harness
connector, use the J 35616
connector test adapter kit . Using this kit prevents damage to the
harness/component terminals. Refer to
Using Connector Test Adapters
in Wiring Systems.
| • | DTC P1518 sets if the battery voltage is low. If the customers 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 such as cruise and 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 or PCM serial data circuits for intermittent connections. |
| • | The following problems may cause an intermittent: |
| - | Poor connections -- Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| - | Corrosion |
| - | Mis-routed harness |
| - | Rubbed through wire insulation |
| - | Broken wire inside the insulation |
| - | Inspect the TAC module connectors for signs of water intrusion. When this occurs, multiple DTCs should be set and no circuit or component problems can be located. |
| • | When the TAC module detects a problem within the TAC System, more than one TAC System related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual problem may correct more than one DTC. Keep this in mind when reviewing captured DTC info. |
| • | For an intermittent condition, refer to Symptoms . |
THROT CONT Fuse Underhood Electrical Center Terminal Identification | |||
|---|---|---|---|
Front of Vehicle | |||
Left Side of Vehicle | Ignition Voltage | TAC Module | Right Side of Vehicle |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if the IGN relay is suppling a voltage to the THROT CONT fuse. If only one side of the fuse is powered, the fuse is open. Replace the fuse after you perform the diagnostic table.
-
This step determines if an internal PCM Processor is failing.
If this DTC does not Fail This Ignition, continue to monitor this DTC status while moving related harnesses and connectors. Refer to Diagnostic Aids if the harness movement causes this DTC to set.
-
Increasing the engine speed to 3000 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. 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 and this DTC sets. This occurs because one set of the transistors are low 0 volts and the other set are high B+. Therefore, if one 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. Refer to Diagnostic Aids if the harness movement causes this DTC to set.
-
This step determines if the ignition feed circuit to the TAC is shorted to ground. If the circuit is shorted to a ground, repair the grounded circuit and replace the THROT CONT fuse.
-
When a condition is detected within the TAC system, more than one TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. It is possible that locating and repairing one individual condition may correct more than one DTC. Keep this in mind when reviewing captured DTC info.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Does the test lamp illuminate on at least one side of the fuse? | -- | Go to Ignition Relay Diagnosis | ||
3 |
Does the test lamp illuminate? | -- | ||
Install a scan tool. Is DTC P0606 is also set? | -- | |||
|
Important: If the driver information center is displaying Reduced Engine Power, go to step 6.
Did this DTC fail this ignition? | -- | Go to Diagnostic Aids | ||
6 |
Important: Disconnecting the throttle actuator motor harness connector causes additional DTCs to set. Are both circuits above the specified value? | 8 V | ||
7 |
Is the resistance within the specified range? | 0-5 ohms | ||
8 |
Is continuity indicated? | -- | ||
Is continuity indicated? | -- | |||
10 |
Is continuity indicated? | -- | ||
11 |
Is continuity indicated? | -- | ||
12 |
Are both circuits near the specified value? | 0 V | ||
13 |
Does the DMM display continuity from either throttle actuator motor circuit to any other TAC module circuit? | -- | ||
14 | Test for continuity from the TAC module ground circuit to battery ground using the DMM. Is continuity indicated? | -- | ||
15 | Measure the voltage at the serial data circuits at the TAC module 16-way harness connector using the DMM. Are both serial data circuits within the specified voltage range? | 0-4.5 V | ||
16 |
Does the DMM display OL for both circuits? | -- | ||
17 |
Is the continuity within the specified range for either circuit? | 0-5 ohms | ||
18 |
Does the DMM display continuity from either serial data circuit to any other circuit? | -- | ||
19 | Measure the voltage of both serial data circuits at the TAC module 16-way connector using the DMM. Is voltage indicated on either circuit? | -- | ||
20 |
Is continuity indicated for both serial data circuits? | -- | ||
21 |
Is the voltage at the specified value? | 0 V | ||
22 | Repair the TAC module ignition feed circuit for a short to ground. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
23 | Repair the throttle actuator motor circuit for a short to ground on the affected circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
24 | Repair the TAC module ignition feed circuit for an open. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
25 | Repair the throttle actuator motor circuits for a short to voltage on the affected circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
26 | Repair the TAC module ground circuit for an open. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
27 | Repair the serial data circuit for a short to ground on the affected circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
28 | Repair the serial data circuit for a short to voltage on the affected circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
29 | Repair the serial data circuit for an open on the affected circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
30 | Repair the circuits that display continuity. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
31 | Repair the ignition feed circuit for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
32 | Replace the TAC module. Refer to Electronic Throttle Actuator Control Module Replacement . Is the action complete? | -- | -- | |
33 |
Important: Program the replacement PCM. Replace the PCM. Refer to Electronic Throttle Actuator Control Module Replacement . Is the action complete? | -- | -- | |
34 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK | |
