P1516 Code in GMC Chevy: Meaning, Causes and Fix
In this article, you’ll learn about the P1516 code in GMC Chevy and Cadillac. P1516 trouble code is a part of the vehicle’s ‘Throttle Actuator Position Performance’. P1516 trouble code does not apply to all vehicles. It’s a manufacturer-specific trouble code that is applied to GMC and Chevrolets like Yukon, Cadillac Escalade, Acadia, Colorado, Trailblazer, Silverado, Tahoe, and Mailbu.
So if you’re experiencing this P1516 trouble code problem in your vehicle, read this guide till the end as I have discussed the exact meaning, symptoms, and causes of the P1516 code in your Chevy vehicle. Moreover, I will also explain how to fix the issue that is causing the P1516 trouble code in your vehicle.
P1516 code in Chevy and GMC vehicles can be fixed by the following actions:
- Cleaning the throttle plate if it is binding
- Replacing the throttle body
- Diagnosing throttle position (TP) sensors
- Look for an open or shorted wire harness in the TAC module and throttle body connector
- Replacement of TAC module if its terminals are damaged
Bonus Read: P0128 Code
What Does Engine P1516 Code Mean?
The exact meaning of the P1516 code is that there is a problem with the Throttle Actuator Control (TAC) module of your engine that affects the Throttle Actuator Position Performance. P1516 is an OBD2 diagnostic code in some GMC and Chevy vehicles.
P1516 trouble code is set when the power control module (PCM) detects an unstable throttle position for greater than 0.5 s. This happens when indicated throttle position does not match the predicted throttle position of the throttling butterfly valve in the engine’s throttle body.
As soon as the ECM sets the P1516 code, the vehicle goes into the reduced power mode by commanding the TAC module. TAC module has two wire harness connections. One is dedicated to the Accelerator pedal position sensor and the other for the PCM connection and throttle operation.
When a vehicle goes into the reduced power mode, it will not be able to travel above a certain speed. This is to ensure that the engine components do not undergo serious failure at high speeds.
The predicted throttle position is based on the accelerator pedal position (APP) sensor, and some other limiting factors. When a driver depresses the gas pedal, this changes the value of the pedal position sensor. The sensor sends the reading to the ECM, which then commands the TB(throttle body) actuator to change the position of the throttle valve.
On the throttle body, two TP sensors are located that verify the movement of the throttle plate and that it is in the proper position.
Predicted throttle position is compared with the actual throttle position. The two values should be within a calibrated range of each other. The power control module (PCM) and TAC module of the engine repeatedly monitor the predicted and actual throttle position. PCM will throw the P1516 code if it detects an out-of-range condition between the predicted and the actual throttle position.
Also Read: Oil Problems In Chevy Engines
What Is Throttle Actuator Control Module?
Throttle actuator control module is responsible for opening and closing the throttle valve/plate in the throttle body through its actuator when it receives electric signals from the ECM. TAC module is like a black box you will find on the driver-side firewall under the hood.
The throttle actuator control module (TAC) is like an engine control module (ECM). ECM is a control center of TAC that determines the driver’s intent by calculating the response from the acceleration pedal and determining the appropriate throttle response.
The Throttle Actuator Control (TAC) Module receives input from the accelerator pedal position sensors and sends these signals to the ECM. The ECM converts them into a pulse width modulated signals and sends them to the TAC module. ECM and TAC module are connected via a dedicated serial data circuit.
The TAC control module receives the pulse width modulated voltage signals from the ECM through a wiring harness connecting TAC and ECM to set the correct positioning of the throttle plate/valve.
TAC module uses the following circuits to receive voltage signals from the ECM:
- Motor Control 1
- Motor Control 2
To monitor the TAC module data, two processors are located within the ECM. These processors share data with the ECM to verify that the indicated throttle position is correct.
Note: Pulse-width modulated voltage is a high frequency ON/OFF signal.
How P1516 Code Is Set?
Anything that can delay the time during which the throttle body valve should move to a certain angle can cause the P1516 code to set. This can be caused by deposits in the throttle body or intermittent voltage signals due to the damaged wiring harness connector to the throttle body.
Basically, when you step on the gas pedal, this changes the value of the pedal position sensor, which commands the TB(throttle body) motor to move. The two sensors on the throttle body record the positions as the valve moves. These sensors send their reading to the ECM, If ECM detects that the throttle valve is not in the proper position, the P1516 code is set.
Possible Causes of P1516 Code in Chevy
- Wires going into the throttle body are damaged
- Shorts or bents anywhere in the throttle control module wiring
- Water intrusion on the connectors of TAC module
- Loose wiring crimp at the throttle body connector
- Throttle body sensors have gone bad
- Pedal gas sensor or assembly is faulty
- Throttle body is damaged (throttle plate is not returning to its resting place quickly enough when you release a gas pedal)
- Throttle body is not cleaned
- TAC module is faulty
- PCM is not programmed
- Low battery voltage i.e. between 4 to 5 volts
- Ground connection between the engine wiring harness and the rear of the engine block.
Conditions for Running the P1516 Trouble Code
You must have the OBD2 tool to run the diagnostic trouble code under the following conditions:
- The ignition is ON i.e. in the run or crank position
- The ignition voltage is greater than 6.5 volts
- The system is not in the battery saver mode
- DTCs P0068, P2119, and P2176 are not set
If the system is in battery saver mode, TAC module removes the voltage from motor control circuits, thus removing the motor’s idle current draw and allowing the throttle to return to its spring-loaded default state
Conditions for Clearing the Trouble Code
When ECM sets the P1516 trouble code, the check engine light also turns on. However, there are certain conditions in which the trouble code is cleared:
- The ECM turns off the check engine light after 3 consecutive ignition cycles that the diagnostic runs and does not fail
- A current trouble code, the last test failed, clears when the diagnostic runs and passes.
- A history trouble code clears after 40 consecutive warm-up cycles if no failures are reported by this or any other emission-related diagnostic
- Clear the check engine light and trouble code with an OBD2 scan tool
Steps To Diagnose P1516 Trouble Code In Chevy
1. Analyze the Readings of Throttle Position Sensors
Use the OBD2 scan tool to observe the readings of Throttle Position (TP 1 and TP) sensors. These two sensors are located on the shaft of the throttle butterfly valve. TP sensor 1 signal voltage is near the low voltage reference. The voltage of the TP 1 sensor increases nearly to 5 volts as the throttle plate is opened.
The TP sensor 2 signal voltage at the closed throttle is near the 5-volt reference and decreases as the throttle plate is open.
By slowly depressing and releasing the accelerator pedal, you should see the readings of TP 1 and TP 2 sensors increase when depressing the pedal and decrease when releasing the pedal.
If you see the change in TP sensor readings on the scan tool, you should proceed to the next step i.e. observing the movement of the throttle body valve.
If the scan tool does not show any change in the parameters of TP sensors, the chances are that the harness connectors at the throttle body, TAC module, and pedal assembly have undergone water intrusion or the wires at the connector have been pulled out.
Moreover, a low voltage of the battery can also cause the TP sensors not to show any reading on the scan tool.
2. Analyzing the Movement of Throttle Body Valve
The throttle valve is spring-loaded and is slightly in an open position. This is its rest position. On the OBD2 scan tool, there is a throttle body control function to operate the throttle valve. This function operates the throttle valve through the entire range in order to determine if the throttle actuator control (TAC) system operates correctly.
The following conditions indicate the healthy throttle valve functioning:
- The throttle valve should be open 20-25%.
- The throttle valve should not be completely closed or completely opened more than 25%.
- The throttle butterfly valve should move open and to the closed position under the normal spring pressure without binding.
- The throttle should not be free to move open or closed without spring pressure.
Note: When you operate the throttle body through the scan tool, it can cause additional trouble codes to set. Ignore those trouble codes during your diagnosis.
You can also test the throttle valve manually without using a scan tool. But make sure that the ignition is turned off, the air duct is removed and the throttle body harness is disconnected before inserting fingers into the throttle bore. With your hand, slowly open the throttle plate to the wide open position and back to the closed position several times and see if the throttle plate moves smoothly without binding in both directions.
If the throttle valve is moving with binding, chances are that there are carbon deposits inside the throttle body that are not letting the valve move freely under the spring force. If the throttle valve sticks somewhere due to the carbon or varnish deposits, it will not be able to reach the predicted position within a calculated time. As a result, the ECM will set the P1516 code in your Chevy vehicle.
If after cleaning the throttle body, the problem is not fixed, you might have to replace the throttle body. Make sure to perform a procedure of relearning or resetting the new throttle body so that it is properly calibrated.
To relearn throttle body:
- Start and idle the engine in PARK for 3 minutes.
- With a scan tool, monitor desired and actual RPM.
- The ECM will start to learn the new idle speed and the desired RPM should start to decrease.
- Ignition OFF for 60 seconds
- Start and idle the engine in PARK for 3 minutes
- After the 3-minute run time, the engine should be idling normally
After performing relearn procedure for the new throttle body and the engine still does not run within the normal idle speed, it will be mandatory to drive your vehicle above 45 mph (70 Km/h) including several decelerations.
Also, ensure that after driving the vehicle, let the engine idle for a minimum of 5 minutes. If the engine has returned to normal idle speed, the relearn procedure is completed. If the idle speed is still erratic or incorrect, restart the idle relearn procedure.
Note: During the drive cycle during idle speed relearn, the check engine light may come on with idle speed trouble codes. If idle speed codes are set, clear codes so the ECM can continue to learn the new throttle body.
Watch the below video to learn more:
Throttle body can also be relearned with a bi-directional scan tool. HP tuners can work. You can go to nearby auto shop to get it done.
You have to perform the following steps:
- With a scan tool, select the Ignition ON and Engine OFF.
- Perform the Idle Learn Reset in Module Setup on the scan tool.
- Start the engine and monitor the TB Idle Airflow Compensation parameter. .
- The TB Idle Airflow Compensation value should equal 0 % and the engine should be idling at a normal idle speed.
- Clear the DTCs.
3. Inspect the Harness Connectors on the Throttle Body
On the side of the throttle body, there is a wiring harness connector having a purple clip. Remove purple clips from the backs of the connector of the throttle body and tug on each wire to ensure that none have pulled out of the terminals. Also, make sure that there is no corrosion and moisture inside the connector.
You can watch the below video for a better understanding.
Moreover, check if there is any intermittent break in the brown and yellow wire in the wiring harness to the throttle body by watching for insulation stretch while pulling on the wire a few inches back from the connector. Also, see if the yellow and brown wires are broken inside the insulation 1 inch to 4 inches from the throttle body connector.
4. Test The Throttle Body Motor Control Circuit For Short To Ground and Short to Voltage
The throttle valve is operated by the motor that receives electric signals from the TAC module. If there are shorts anywhere in the throttle control system wiring, PCM will be powered up before the TAC module. As a result, there will be some delay in the actual and predicted throttle valve position. Due to this reason, the PCM could set the P1516 trouble code.
Before proceeding further, you have to understand the throttle body motor control circuit. If you remove the harness connector from the throttle body as advised in the above step, you will observe 8 connections divided into two rows.
The above row on the connector is labeled from A to D and the below row from E to H.
Here is the meaning of each wire color:
- A: (Yellow wire) TAC Motor Control 1.
- B: (Black with White stripe wire) Low Reference (Sensor Ground).
- C: (Brown wire) TAC Motor Control 2.
- D: (Black) Low Reference (Sensor Ground).
- E: (Light Blue with Black wire) 5 Volt Reference.
- F: (Purple) TP Sensor 2 Signal.
- G: (Dark Green) TP Sensor 1 Signal.
- H: (Grey) 5 Volt Reference.
To open the throttle plate, the A circuit becomes the voltage source and the C circuit becomes the ground. To close the throttle plate, C becomes the voltage source and A (motor control 1 circuit) becomes the ground.
Chevy 3.6L engines have a 6-pin throttle body connector instead of an 8-pin. The upper row is designated from A to C and the lower is designated from D to F.
Here is the meaning of each pin:
- A: TAC Motor Control 2
- B: TAC Motor Control 1
- C: Low Reference
- D: TP Sensor 1 Signal
- E: 5-volt reference
- F: TP Sensor 2 Signal
In engines, there can be short to voltage i.e. when two live wires contact, or short to ground i.e. when there is contact between the live wire and ground wires of the engine.
In Chevy, the ground wiring harness consists of a black wire, top, right rear of the engine block just behind the intake. You should check the ground connection between the engine wiring harness and the top, right, and rear of the engine block, particularly the engine harness ground at the top right of the block just behind the intake. Also, check the black wire that runs on the passenger side of the engine. The location where it is mounted is where the PCM is grounded. Another important thing is the ground strap which you will find on the driver-side firewall.
I found this video helpful:
To test the TAC Motor circuit, you have to use DMM. For a better understanding, check out the below video:
To inspect the harness connector of the Throttle body, follow these steps:
- Turn off the ignition
- Remove the throttle body harness connector.
- Probe the throttle actuator control (TAC) motor control 1 circuit with a test lamp connected to the ground. Repeat the same process for the TAC motor control 2 circuit. You can use a battery negative terminal as ground. Turn On the ignition.
- If the test lamp illuminates, turn off the ignition and disconnect the ECM harness connector that contains the TAC motor control circuits. Probe the TAC motor control 1 and 2 circuits on the ECM connector with the test lamp connected to the ground. If the test lamp illuminates, repair the short to voltage on the circuit where the test lamp remained illuminated in step 3. If the test lamp does not illuminate, check any loose connections or the terminal tension at the ECM connector.
- If the test lamp does not illuminate in step 3, probe the throttle actuator control (TAC) motor control 1 circuit with a test lamp connected to the battery positive terminal. Repeat the same process for the TAC motor control 2 circuit. After connecting the test lamp, turn On the ignition.
- If the test lamp illuminates, turn off the ignition and disconnect the ECM harness connector that contains the TAC motor control circuits. Probe the TAC motor control 1 and 2 circuits on the ECM connector with the test lamp connected to the battery positive terminal. If the test lamp illuminates, repair the short to ground on the circuit where the test lamp remained illuminated in step 3. If the test lamp does not illuminate, check any loose connections or the terminal tension at the ECM connector.
- If the test lamp does not illuminate or flashes On and then OFF in steps 3 and 4, test for a poor connection or terminal tension at the throttle body connector.
Some Intermittent Electrical Faults in Circuit That Can Cause the P1516 Code
Here are the following intermittent electrical faults in the circuit that can set the P1516 code due to the loss of communication between PCM and TAC module:
- Broken wiring inside insulation
- Poor connection between the male and female terminal at a connector Poor terminal to wire connection
- Crimping over the wire insulation rather than the wire itself
- Corrosion in the wire to terminal contact area, etc. Pierced or damaged insulation can allow moisture to enter the wiring causing corrosion.
- Swollen and stiff sections of wire in the suspect circuits.
- Wiring which has been pinched, cut, or its insulation rubbed against a surface may cause an intermittent open or short as the bare area touches other wiring or parts of the vehicle
So, that was all about the causes and troubleshooting of the P1516 code. Apart from inspecting the throttle body and TP sensors, you should also check the ground connections for intermittent faults in the electrical circuit. Due to the intermittent faults, the PCM and TAC module cannot properly communicate with each other, due to which the ECM could set the P1516 code.
So, to fix the P1516 Code in Chevy or GMC vehicles, first, you should check whether the throttle body is clean or clogged with carbon deposits. You can use LRC Throttle Body Cleaner. After that, inspect the throttle body connector and the connector at the TAC module for loose connections or water intrusion that could cause corrosion at the terminals.