Remote starting your pre-2008 GM truck relies on a specific method involving the OBDII port. Unlike newer vehicles, these trucks use the OBDII data wire to initiate a diagnostic start mode. This process bypasses the Passlock anti-theft system for testing purposes. Let’s delve deeper into how this Obdii Remote Start system functions and the necessary modifications for installation.
Understanding Diagnostic Start Mode and OBDII Remote Start
The OBDII port on your GM truck uses the J1850 data wire for communication with diagnostic tools and programmers. This same wire is utilized by some remote start systems to trigger diagnostic start mode. However, this method can cause interference. A more reliable approach involves using relays to simulate the key data, effectively mimicking a manual start without engaging diagnostic mode. This ensures seamless operation and avoids conflicts with the vehicle’s data communication.
Resistive Immobilizer System in Pre-2007 GM Trucks
Trucks manufactured before mid-2007 employ a resistive immobilizer system. Instead of a chipped key, these systems utilize a resistor in the ignition cylinder with a specific resistance value (R Code). This code can be measured using a multimeter, following specific instructions (as illustrated in the provided diagram). A trim potentiometer (trim pot) can then be adjusted to match the truck’s R Code.
How the OBDII Remote Start System Works
When the remote start is activated, the status wire energizes, activating relays that interrupt the factory R Code wire. The trim pot’s matched R Code is then injected into the Passlock module. This fools the system into believing the correct key is present, allowing the engine to start. This setup mimics a traditional key start, ensuring compatibility and avoiding potential conflicts.
Required Modifications for Installation
This method has a drawback: disconnecting the factory R Code wire impacts door lock and door pin functionality. To address this, installers typically:
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Bypass Door Pin Monitoring: Diodes are used to bypass the factory door pin monitoring, similar to installations on 2001 model year trucks. Alternatively, tapping into the dome light wire can achieve the same result.
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Control Door Lock Motors: Five-wire connections with two relays, or a single 451M relay, are required to control the door lock motors independently. This restores proper door lock operation.
Communicating with Your Installer
A knowledgeable installer will understand these requirements. Providing them with this information ensures a proper and functional obdii remote start installation. With the correct modifications, your pre-2008 GM truck will start remotely without interfering with the vehicle’s other systems.
Conclusion
OBDII remote start on pre-2008 GM trucks requires a specific approach utilizing relays and a trim pot to bypass the Passlock system effectively. While this involves some modifications to door lock wiring, a skilled installer can ensure a seamless and reliable remote start experience. This method avoids potential diagnostic mode conflicts, making it a reliable solution for these vehicles.
