| 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 DTC sets.
Conditions for Running the DTC
| • | The ignition switch is in the crank or the run position. |
| • | The ignition voltage is greater 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 met for less 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
| • | 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 that may have set from the low battery voltage condition from the memory. |
| • | 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 the cruise, or the 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. When water intrusion occurs, multiple DTCs could be set with no DTC 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 that run continuously on this system. Locating and repairing 1 individual problem may correct more than 1 DTC. Keep this in mind when reviewing captured DTC info. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
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.
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This step determines if the IGN relay is suppling a voltage to the THROT CONT fuse.
-
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 is near 0 volts, and the other set is at high B+. Therefore, if 1 set of transistors is 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.
-
When the TAC module detects a condition within the TAC system, more than TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting the components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the test lamp illuminate on at least 1 side of the fuse? | -- | Go to Step 3 | Go to Ignition Relay Diagnosis | |
3 |
Does the test lamp illuminate? | -- | Go to Step 22 | Go to Step 4 |
4 | Install a scan tool. Is DTC P0606 also set? | -- | Go to Step 5 | |
|
Important: If the Driver Information Center is displaying Reduced Engine Power, go to Step 6.
Does the scan tool indicate this DTC failed this ignition? | -- | Go to Step 6 | Go to Diagnostic Aids | |
6 |
Does the DMM indicate voltage on both circuits above the specified value? | 8 V | Go to Step 12 | Go to Step 7 |
7 |
Does the DMM indicate continuity to ground? | -- | Go to Step 10 | Go to Step 8 |
8 |
Does the DMM indicate continuity to ground? | -- | Go to Step 9 | Go to Step 11 |
9 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 24 |
10 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 24 |
11 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 24 |
12 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 13 |
13 |
With a DMM, Test for a short between each throttle actuator motor control circuit and all other TAC module circuits. 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 | With a DMM, test for an open or for high resistance in the TAC module ground circuit. 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 | With a DMM, test for voltage on the serial data circuits at the TAC module 16-way harness connector. 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 |
Does the DMM indicate OL for both circuits? | -- | Go to Step 20 | Go to Step 17 |
17 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 18 |
18 | With a DMM, test for a short between both serial data circuits and all other circuits at the PCM and TAC module harness connectors. 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 | With a DMM, test for a short to voltage on both serial data circuits at the TAC module 16-way connector. 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 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 21 |
21 |
Does the DMM indicate voltage at the specified value? | 0 V | Go to Step 25 | Go to Step 24 |
22 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 23 |
23 |
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 |
Does the DTC run and pass? | -- | Go to Step 29 | Go to Step 2 |
With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | ||
