For the EHPAS module, the reference material I have shows that one message is required to turn it on. There's a single bit in that message which, if set, tells the EHPAS motor to start running. The EHPAS also listens for two other values - Road Speed and Steering Angle rate of change. Both get used to determine how fast the pump should run. If the speed is low, the pump speeds up. If the steering wheel is turned suddenly, the pump speeds up. In all other situations, the pump slows down.
Broadcast messages look like the following - a header that is used for priority and arbitration, and then a bunch of data. Determining which module sends which messages is an exercise in reverse engineering. I was pulling fuses or disconnecting modules and seeing which messages disappear.
00 00 00 80 27 10 75 30 01 30 77
This message comes from the
PCM, but it uses data from teh Steering Angle Sensor in the Clockspring.
The 00 00 00 80 is actually a 29 bit address. As an 11 bit address it looks more like 080.
The next 8 bytes are the data in hex.
2710h is 10,000 decimal. I think the actual steering angle would go here, but the XR4 doesn't populate it. It hasn't changed in all of the testing I've done.
7530h is 30,000 decimal and is the steering rate of change. Turn left and the value increases, depending on how fast it is turned. And turn right and the value decreases below 7530h.
The very last field, 77, is continuously incrementing, so looks like it gets used to index the messages. Indexed messages means it can detect when messages get dropped, and also make it hard to 'inject' other messages into the stream.
Which leaves 0130h. In binary thats 0000 0001 0011 0000. My documents suggest that that two those bits set to 1 is telling the EHPAS to turn on. There are 3 other bits there potentially telling me whether the Steering Angle Sensor is fine or has been initilaised.
There will no doubt be other messages involved, but what I see in the Fiesta doesn't match withmy documents just yet. For example, my documents say 080 should also have vehicle speed - but I haven't seen it. HOWEVER, so far I have only done my speed tests with the wheels off the ground on my hoist - which the
ABS module doesn't like having wheels all go different speeds. I'll do some down the road tests shortly. WHat is encouraging is that the message that is SUPPOSEDto show speed for the INsrument cluster, is also showing 2710h. However, I did see the speedo dial move while on the hoist. More attention andanalysis required.
I DO, however, have a possible broadcast message that the EHPAS module might send, that includes a 'pump fail' message. The message is 240h - and is not currently present in the car, which makes sense. I have a Focus EHPAS pump here, and will attemp to power it up in the coming weeks and hook it up to a CAN tool to see if it is issuing broadcasts. But it's that Pump Fail message that may be responsible for lighting up the 'EHPAS' light on the instrument cluster, in the lower right of the Tacho dial.
Luke