Communication Interface and Cable Details
The Range Rover Electronic Air Suspension (EAS) communications interface is a very simple three wire transmit (Tx), receive (Rx) and ground (Gnd) arrangement. These three wires can be connected to any RS-232 PC serial port interface and establish a communications session very easily without any level shifting. To further simplify matters, the Range Rover EAS is the only Electronic Control Unit (ECU) on these communication wires.
Interface Cable Details
The hardware serial interface between the PC and the EAS, can be constructed using off the shelf parts for under 20 USD. The parts required for this interface cable can be obtained from www.mouser.com and www.OBD2cables.com,
Part Numbers Needed (You need either 1 & 3 or 2 & 3) and Links to Suppliers:
1. OBDII Cable http://www.obd2cables.com/products/
OBDII Pass-Through Cable
2. OBDII cable http://www.mouser.com
Unsealed 16pin male OBDII
Unsealed Terminals Male OBDII 829-12047581
3. DB9 Serial http://www.mouser.com
AIM D-Sub Connector 9 Pos Solder Female 601-40-9709S Approx $0.44
AIM D-Sub Hood 601-40-9709HX Approx $0.70
Once the parts are obtained, a few simple solder
need to be made. For example, if
you opt for the DB9 Serial connector, connect pins 2(Rx),
3(Tx) and 5(Ground) on that connector to the OBDII pins 11(White)(Tx),
respectively. These OBDII pins go straight to the EAS ECU communication
Make sure and double check the wire color to pin map from the OBDII
through connector. The manufacturer could change the wire colors
notice. This is what your completed cable will look like:
Cable using options 1 & 3
Cable using options 1&2
EAS ECU Microprocessor and Programming Details
The microprocessor in the EAS ECU is a very commonly used Motorola 68HC705B series single chip microprocessor. This is great news for us, as it limits the possible serial protocol communication options. The EAS ECU operates the serial interface at a very low speed of 600 bps, using 8 data bits, no parity, 1 stop bit and no hardware control (8,N,1, None). The data transmitted and received across the serial interface is in a Hexadecimal format, 0xF7, 0xF8, 0xF9, 0xFA, etc…
Any terminal program or serial protocol analyzer
will work for this serial interface, providing it meets the above
settings. The program I use is called “Realterm” and is considered
This program can be downloaded from http://realterm.sourceforge.net/.
should be “Hex + Space” and “Half Duplex”. Port settings should be
“Parity None”, “Data Bits 8”, “Stop bits 1”, “Hardware None”. Under the
tab, enter a HEX address (0xF7) in the blank field and press “Send
The EAS should respond with a HEX value.
The ultimate goal of this cable PC interface is to reset the EAS microprocessor. Currently, we do not have the ability to actually reset the EAS but have made some significant advances. With this physical and software interface, more people will be able to test this and move us towards a more complete solution. So far we know a few memory address locations inside the Motorola Processor and are trying to understand the message framing necessary to change those locations. For example, the following memory locations hold the Diagnostic Troubleshooting Codes (DTC), (0xF7, 0xF8, 0xF9, 0xFA, 0xFB, 0xFC). This information is one step closer to resetting the EAS but we still need to know what to do with those memory locations. Eventually a simple string of HEX commands will be used to reset the EAS system. A logical assumption would be that the memory address locations of the DTC codes would need to be surrounded or framed by other function HEX codes.
RSWSolutions.com is the website of Range Rover enthusiast Storey Wilson who cracked the EAS interface and developed software for calibrating and resetting it.
Sourceforge.net is the host for the freeware -- you can download it from this site. The software can read and reset faults, as well as calibrating the air suspension. The Range Rover specific page for free downloads is at this link
Range Rover Diagnostics Forum: A discussion forum (including manufacturers) all about Range Rover computer diagnostic problems and solutions.
See also the page on Clearing EAS Faults using a Notebook Computer and Free Software for a typical user experience.