Encountering a “Trouble Negotiating Protocol” error when you try to read your 1996 Grand Caravan’s computer with an OBD2 scanner can be frustrating. This message essentially means your scanner and your minivan’s engine control unit (ECU) are having trouble communicating. Let’s break down what this means and how you might resolve it.
The On-Board Diagnostics II (OBD2) system is designed to allow scanners to easily access vehicle diagnostic information. However, the “trouble negotiating protocol” error indicates a breakdown in this communication process right at the initial handshake. Think of it like two people trying to speak different languages – they can’t understand each other, even if they are both present.
Several factors can contribute to this communication issue specifically on a 1996 Grand Caravan:
-
Scanner Compatibility: While OBD2 was becoming standardized in 1996, early implementations could have slight variations. Some older or very basic OBD2 scanners might not perfectly align with the communication protocol used by your ’96 Grand Caravan’s ECU. It’s possible your scanner is simply not fully compatible with the specific protocol used by Chrysler at that time. Trying a different OBD2 scanner, especially one known to work well with older Chrysler vehicles, is a good first step.
-
OBD2 Port Issues: The OBD2 port itself can be the source of the problem. Check the port under your dashboard for any signs of damage, bent pins, or corrosion. A faulty connection here will prevent the scanner from properly interfacing with the vehicle’s computer. Ensure the scanner is firmly plugged into the OBD2 port.
-
Vehicle’s Computer (PCM/ECU) Problems: Less commonly, the issue might lie with the Grand Caravan’s Powertrain Control Module (PCM) or Engine Control Unit (ECU). If the computer itself has a fault in its communication circuitry, it won’t be able to respond correctly to the scanner’s requests. However, consider this as a possibility after ruling out scanner and port issues first.
-
Wiring Problems: The wiring between the OBD2 port and the PCM is crucial. Damage to this wiring harness, although less frequent, could interrupt the communication pathway.
In summary, when your OBD2 scanner displays “Trouble Negotiating Protocol” on your 1996 Grand Caravan, begin by verifying scanner compatibility and inspecting the OBD2 port for damage. Ruling out these common issues will help you narrow down whether the problem lies with the vehicle’s computer system itself. If you’ve tried multiple scanners and checked the port without success, it may be time to consult a professional mechanic who can diagnose deeper electrical or computer issues.
