Installing a remote starter can add convenience and comfort, especially during harsh weather conditions. Many modern remote starter systems utilize the OBD2 port for communication and installation, leading to a seemingly straightforward plug-and-play experience. However, for owners of older GM trucks, particularly those manufactured before 2008, the OBD2 port’s role in remote starter installation and functionality can be more complex and require a different approach. This article will delve into why some remote starters that rely on the OBD2 port might encounter compatibility issues with these older GM models and explore a reliable alternative solution.
The OBD2 Port and Remote Starters: A Common Misconception
The On-Board Diagnostics II (OBD2) port is a standard interface in most modern vehicles, primarily used for diagnostics and data retrieval. It’s become increasingly common for remote starter systems to utilize this port for sending commands to the vehicle’s computer system. This method often simplifies installation, as it can reduce the need for extensive wire splicing. Many assume that simply plugging a remote starter module into the OBD2 port is universally compatible across all vehicles. However, this assumption overlooks the nuances of different vehicle architectures and how they handle remote start functionalities.
The Challenge with Older GM Trucks (Pre-2008)
For certain older GM trucks, specifically models around 2005 up to approximately 2008 (and potentially earlier), the OBD2 port is utilized in a unique way for remote starting. These vehicles are designed to enter a “diagnostic start mode” when a remote start command is initiated via the data wire at the OBD2 port. This diagnostic mode is essentially a troubleshooting feature implemented by GM, designed to bypass the Passlock security system for testing purposes.
The critical point of conflict arises because this same data wire (J1850) is also used by diagnostic scanners, programmers, and other OBD2 tools to monitor vehicle data during normal operation. Unfortunately, this data wire is not designed for simultaneous dual duty – functioning both for diagnostic mode remote starting and regular data communication. Attempting to use an OBD2-port remote starter that relies on this diagnostic mode on these older GM trucks can lead to several problems, including:
- Interference with other OBD2 devices: The remote starter’s constant communication through the data wire can disrupt the functionality of scanners or programmers plugged into the OBD2 port.
- Potential system conflicts: Forcing the truck into diagnostic mode for remote start might interfere with other vehicle systems or create unintended consequences.
- Limited functionality: The reliance on diagnostic mode might restrict certain remote start features or vehicle operations.
The Relay-Based Solution: Simulating Key Operation
To overcome these OBD2 port limitations on older GM trucks, a more robust and reliable solution involves bypassing the diagnostic start mode altogether. This is achieved by using relays to simulate the actual key turning process, effectively mimicking the signals that occur when you manually start the vehicle with the key in the ignition.
Instead of commanding the truck into diagnostic mode through the OBD2 data wire, this relay-based system focuses on replicating the key data. As far as the truck’s computer system is concerned, it is being started by someone physically in the driver’s seat turning the key. This approach completely bypasses the need to utilize the OBD2 data wire for remote starting commands, eliminating the potential conflicts and limitations associated with diagnostic start mode.
How the Relay System Works with Passlock and Resistors
Trucks manufactured prior to the mid-2007/2008 model year often employ a resistive immobilizer system, commonly known as Passlock. Unlike newer systems with chip-embedded keys, Passlock systems in these older GM trucks rely on a resistor within the ignition cylinder. This resistor has a specific, known value (R-Code).
The relay-based remote start solution cleverly integrates with this Passlock system:
- R-Code Identification: The resistor value (R-Code) of the vehicle needs to be determined. Instructions for reading this value are typically available and involve measuring resistance at specific points.
- Trim Pot Implementation: A trim potentiometer (trim pot), which is a type of adjustable resistor, is set to match the R-Code value of the vehicle’s ignition resistor.
- Relay Activation Sequence: When the remote start is engaged, the first signal activated is typically a status (-) wire. This signal triggers relays that are connected to both the remote starter’s ignition wire and the Passlock system.
- Passlock Bypass: The relays interrupt the factory R-Code wire from the ignition cylinder and inject the R-Code value from the trim pot into the Passlock module. This action fools the Passlock system into thinking a valid key is being used, allowing the engine to start normally, just as if the key were turned in the ignition.
Addressing Door Lock and Door Pin Considerations
A potential side effect of disconnecting the OBD2 data wire for the relay-based remote start solution is the potential loss of functionality for door locks and possibly door pin monitoring. In some older GM truck models, these features are also routed through that same data wire. Therefore, once this wire is disconnected to implement the relay system, the door locks and door pins might cease to function correctly with the factory wiring.
To restore door lock and door pin functionality, installers need to perform additional wiring:
- Analog Door Pin Wires: Similar to older vehicles like 2001 models, installers will need to tap into the analog door pin wires using diodes. Diodes are electrical components that allow current to flow in only one direction, preventing feedback and ensuring proper signal isolation.
- 5-Wire Door Lock Motor Integration: Door lock motor control requires a “5-wire” configuration. This can be achieved using either two standard relays or a specialized 451M relay module. The 5-wire setup allows for both locking and unlocking commands to be sent to the door lock motors independently, ensuring proper door lock operation with the remote start system.
Guidance for Installers
For professional installers, understanding this relay-based approach is crucial when working on older GM trucks. Presenting this information to your installer can significantly streamline the installation process and ensure a correctly functioning remote starter system.
The key components required for this solution are:
- Relays: A total of four standard relays (or two relays and one 451M module for door locks).
- Diodes: Four diodes (or potentially tapping into the dome light wire as an alternative for door pin sensing in some cases).
- Trim Pot: One trim potentiometer to match the vehicle’s R-Code value.
By implementing this relay-based system and addressing the door lock wiring as described, any remote start issues encountered on these older GM trucks will almost certainly not be related to the OBD2 port or data wire conflicts. This method provides a clean, reliable, and fully functional remote start solution that works in harmony with the vehicle’s existing systems.
In conclusion, while OBD2 port integration offers simplicity for many remote starter installations, it’s not a universally applicable solution, particularly for older GM trucks. Understanding the nuances of these vehicles and employing a relay-based, key-simulation approach is essential for a successful and trouble-free remote starter installation. This method ensures compatibility, avoids potential system conflicts, and delivers the convenience and comfort expected from a remote starter system without compromising other vehicle functionalities.
