ECU Cable Resistors

[V1DL3R]

I'm looking to plug in my ECU and get a read out. There is nothing wrong with the car but I would like to learn how to do this before something goes wrong and help me better diagnose faults in the future.

I need a serial cable and I have read some articles which say you need one with a resistor configuration. This cable seems to be around £60, which is a lot for a small cable for my to essential muck around.

If I wanted to actually map the ECU (which I don't) I would be sending signals from the PC to the ECU, so I get why you would need the resistors. If i'm just reading from it, the signal output should be one way so would a normal serial cable suffice? Anyone know?

[Davie M12]

You can make a cable up for around £10!
schematic is here:

http://www.sbdev.co.uk/Engine_Management_Systems/E...

Some of the part numbers on this schematic are obsolete now but its just a couple of 9 way D types and a bit of cable.

The resistors are to protect the ECU.

Cheers,
David.

[Zoobeef]

Going to order the 2 resistors from Farnells as the part numbers are the same then just modify a normal 9 way cable I think. Probably the easiest way!

[anonymous-user]

Just a standard Dsub (9 way connector) RS232 serial lead, with what looks like added resistors used to make it "special" so you had to buy one from MBE.......


(the resistors form a "bridge" divider, and hence applying half the supply voltage to the pins no 6 & 7. That probably is used to "tell" the ecu that you have plugged in the correct serial cable and it should allow USART coms with the laptop)

(ps. probably don't need expensive 0.1% resistors!, normal 5% ones would almost certainly work unless they have used a ridiculously tight voltage threshold for cable identification)

[Zoobeef]

I'm not normally in the market for buying resistors but they are 91p and £1 so getting different ones cheaper doesnt really matter haha.

Is there an orientation they need to go in as the schematic doesnt say?

Edit: Although VAT and P+P does put the price up a bit!

[V1DL3R]

I've just spoken to one of my friends who is an electrical engineer. He said he would make one up for me to the specs in the link. If anyone else wants one, give me a shout and I will ask him how much he would charge.

Edited by V1DL3R on Wednesday 22 January 17:08

[StreetDragster]

I'll have one

Thanks
Matt

[anonymous-user]

Considering a 5% tollerance one would cost you approx 0.01p, that's "expensive" ;-)

i wonder why they use 1k and 1k05, that's 1000 ohms and 1050 ohms, which gives you a 51.2%/48.8% ratio?

[Davie M12]

Max_Torque said:

Considering a 5% tollerance one would cost you approx 0.01p, that's "expensive" ;-)

i wonder why they use 1k and 1k05, that's 1000 ohms and 1050 ohms, which gives you a 51.2%/48.8% ratio?

Yeah not sure why they spec'd like that but I'd say that's why the tolerance is as tight as with 5% the values could overlap.