It works fine now. All the splices on the car HS CAN bus seem to be within 1 meter of the device. They must have used extra wire and done it that way for a reason. 131 feet is quite long for a 500kbps bus. Is that the limit for a single splice? Is it the maximum length for entire end to end terminated bus?
Not knowing the limitations of my ELM327 1.4b scan tool and using Forscan without a vehicle profile made diagnosis more difficult.
Not really. For 500 Kb/s it is closer to double that length. CAN bus is chosen for Industrial applications for a reason. It is fairly robust protocol.
It is maximum length. Splices donāt matter much unless they are done poorly.
Wiring damage and/or sins are often difficult to resolve. I watched one mechanic trying to use a Fox and Hound type device to trace a suspected broken wire in a bundle that went the length of the vehicle. Problem is, there is crosstalk in the bundle and the tone signal is impressed on any adjacent wire in that bundle making it almost impossible with that approach. I have used TDR device in the past but the shorter the run, the more difficult to find an open using that methodā¦
Any non terminated splice off of the bus will cause the signal to reflect back and distort the signal on the main bus. The devices that connect the bus are not terminated, so that must be why the wire length is so short. The longer the wires are that splice off, the longer the delay and the more distortion that will result. Only the beginning and end of the bus is terminated, so greater length on the main bus does not cause distortion.
I donāt know what you mean by doing a splice poorly.
I see what you are talking about. You mentioned a break in the wire. Repairs require splicing. What youāre describing above, I would call a tap- a separate branch off the bus.
A bad splice will introduce reflections as well and in the worst case, may seriously impair communication speed on the bus.
The Ford diagrams say S106 and such. I assumed that meant Splice number 106. The length of the wires coming off the tap seem to be less than 1 meter.
Now a new problem came up. Car wonāt idle. Have to keep throttle somewhat pressed or it will stall. This started to happen suddenly.
Turns out the battery to chassis ground connection started to fail. The insulation around the connection had gotten hot and was melting. More than 0.7 Volts difference between the engine and chassis with the key turned on.
Fuel economy had been getting worse over the last few months. I wonder if this failing ground connection could have affected engine performance or sensor values?
Apparently there is only one engine to chassis ground, which is the battery negative cable connection. There is no ground strap like in other vehicles.
My Corolla has several ground wires from the engine cylinder head to the chassis. Used to improve the accuracy of the engine computer sensors. they have connectors that can be disconnected to improve repair access. Sometimes I disconnect these wires when performing a repair, then forget to re-connect them, causes weird symptoms.
In your case @TheWonderful90s , it seems like the idle rpm is too low. An idle air control that is sticking seems most likely explanation. What does the idle rpm measure when this problem is occuring?
0 RPM! Itās a throttle by wire vehicle. Itās fixed now, so weāll see if the fuel economy situation changes.