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AutoCodes – GMC – P0816 GMC

P0816 GMC Code - Downshift Switch Circuit

Quick Answer

The Driver Shift Request (DSR) allows the driver to select the desired range of gears for current driving conditions. Common causes include Faulty Transmission Shift Lever, Transmission Shift Lever harness is open or shorted, Transmission Shift Lever circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P0816 GMC indicates Downshift Switch Circuit.
Common causes
Common causes include Faulty Transmission Shift Lever, Transmission Shift Lever harness is open or shorted, Transmission Shift Lever circuit poor electrical connection.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
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Code Popularity 428
How popular is this code, among other codes? Low
What is this?
Table of contents Created and updated by William Orellana on Aug 02, 2022
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Code P0816 GMC Description

The Driver Shift Request (DSR) allows the driver to select the desired range of gears for current driving conditions. The DSR shift system is activated when the gear selector is in the manual position. The DSR system is deactivated in all other range positions. Pressing the plus (+) switch once will command the Body Control Module (BCM) to signal the Transmission Control Module (TCM) to upshift to the next high gear. Pressing the minus (−) switch once will command the BCM to signal the TCM to downshift to the next lowest or previous gear. The TCM will not allow a downshift if the transmission is compromised by over-speeding. The automatic transmission manual shift switch is comprised of three different resistor values in series and two switches. The BCM supplies a 12-volt circuit to the automatic transmission manual shift switch. The signal circuit varies the voltage back to the body control module depending on which switch is depressed. The Diagnostic Trouble Code (DTC) will be set when the BCM detects a stuck On Tap Down switch for 1 second in Park or Neutral or the BCM detects a stuck On Tap Down switch for 10 minutes in any forward gear.
OBDII Code P0816 GMC - Downshift Switch Circuit - AutoCodes.com
P0816 GMC Code - Downshift Switch Circuit
What does this mean?

What are the Possible Causes of the DTC P0816 GMC?

  • Faulty Transmission Shift Lever
  • Transmission Shift Lever harness is open or shorted
  • Transmission Shift Lever circuit poor electrical connection
  • Faulty Body Control Module (BCM)

How to Fix the DTC P0816 GMC?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0816 GMC code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0816 GMC code?

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Information for Specific GMC Models

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0816 GMC Code

1. What does the OBDII code P0816 mean on a GMC vehicle?

P0816 indicates a problem with the downshift switch circuit, which controls gear downshifting in vehicles with manual shift or semi-automatic transmissions.

2. What are the common symptoms of the P0816 code on a GMC?

Symptoms may include the inability to downshift, erratic shifting, the transmission stuck in one gear, or the check engine light being illuminated.

3. What causes the P0816 code to appear in a GMC?

Common causes include a faulty downshift switch, damaged wiring or connectors in the downshift switch circuit, or a malfunctioning transmission control module (TCM).

4. Can the P0816 code cause transmission damage if left unaddressed?

While the code itself may not directly damage the transmission, ignoring it can lead to improper shifting, which may strain the transmission over time.

5. How is the P0816 code diagnosed in a GMC?

A technician will use a scan tool to confirm the code, inspect the downshift switch, check for damaged wiring or connectors, and test the functionality of the TCM.

6. Can a faulty downshift switch trigger the P0816 code in a GMC?

Yes, a malfunctioning downshift switch is a primary cause of this code, as it disrupts the circuit's operation.

7. Is it safe to drive with the P0816 code on a GMC?

Driving may be possible but could be unsafe if shifting becomes erratic or the vehicle is stuck in an inappropriate gear for the driving conditions.

8. How do you fix the P0816 code on a GMC?

Repairs may involve replacing the downshift switch, repairing or replacing damaged wiring or connectors, or reprogramming or replacing the TCM.

9. What tools are needed to troubleshoot the P0816 code on a GMC?

A scan tool, multimeter, and access to the vehicle's wiring diagrams are typically required for diagnosing and repairing this code.

10. Can a software issue in the TCM cause the P0816 code on a GMC?

Yes, a software glitch or outdated TCM programming can sometimes trigger this code and may require a TCM update or reprogramming.

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