illgetyou22

First off i bought the car this way and im new to the urs4 world so bear with me. I have a 1993 urs4 and the last owner told me the ecu was bad. So i bought a used ecu and threw it in. the car cranks and nothing happens i also noticed that i did not hear the fuel pump prim or turn on. So next with the ignition on acc i went to scan the car and i cannot connect to the ecu. I also noticed that when i go to start the can the check engine light does not go on and turn off (not sure if it does this on this platform like the mk3 vw or b5 s4 please correct me if im wrong) Sooo next i follow urs4boys thread and when to check the ecm

I checked pin # 18 (the pin right next to 19) for power and nothing i check over other pins and some are getting power.


Next i checked the fuse for the ecu. with ignition on acc I checked the one in the pic with the red holder (5a) replaced it just in case no but no change then with a test light i checked if the fuse was getting power and it is just because i was a little confused i checked the breaker sitting in the yellow holder that is good too and is getting power. At this point im lost anyone have any advise im not sure what to check from here

UrS4boy

There could be several reasons why your engine isn't starting. However, the first thing is you have to get the ECU to the point that the Check Engine Light comes on when you turn the ignition to RUN (not ACC). To do this, replace the thermal breakers in the panel above the ECU with new/good normal two-blade spade-type fuses. At this point, some of the thermal breakers are failing and it is just easier and not much riskier to replace them with spade-type fuses.

This is what it will look like now:



This is what the UrS6 panel looks like (the factory eliminated the thermal breakers):



This is the call outs for the above:

UrS4boy

Assuming that you have your ECU powered so the check engine light does come on when you turn the ignition key to "ON", then the next things you need to investigate are the G4 crank position sensor, the G28 engine speed sensor and the G40 cam position sensor. The ECU will not power the J17 fuel pump relay until it gets a good signal (>13 RPM) from the G28 engine speed sensor. With the J17 FP relay powered, there should be power to the injectors and the G6 fuel pump. However, the ECU will not fire either the injectors or the coils (via the POSs) until it has a good signal from BOTH the G4 crank position sensor and the G40 cam position sensor.

Go to this link and click on the labels of each of the items I mention above to learn more about how the ECU controls the AAN and all its attached devices:

http://members.shaw.ca/speedtek/UrS%...ice%20Map.html

If you still have questions, come back and we will try to answer them.

illgetyou22

Ok just went out to the garage and took out all the old breakers and fuses and switched them for all new fuses. Still no check engine light and still no power to pin 18 eather

illgetyou22

Ok just went out to the garage and took out all the old breakers and fuses and switched them for all new fuses. Still no check engine light and still no power to pin 18 either

scarman

Are you using a scan tool that you know personally will scan the OBD I system in the UrS4? You are correct that the MIL (check engine light) should illuminate when you turn the key to run as a means to show that the ECU is communicating. Assuming the bulb is good, that is two means that verifies that the ECU is not communicating, either because it or the connection is bad.

Do you know of another UrS nearby that could attempt to use the ECU? That would be the easiest method to move forward in troubleshooting this problem.

UrS4boy

Eather/either. ;>) You gots a problem Houston. Without power to the ECU via Pin 18/55 you aren't going anywhere.

First thing to check now is do you have power in the red wire coming into the red fuse holder? The red wire is connected to the "30" terminal under the driver's side knee bolster. If you don't have 12V in the red wire, the fuse is irrelevant. IF you do have 12V into the red fuse holder, then you will need to figure out if the white wire with a black stripe coming out of that red fuse holder, going to Pin 18/55 on the ECU connector has continuity or if the wire is cut/broken.

The "30" terminal (constant 12V, unswitched) is under the left most "204" relay in this photo:



Factory ECU wiring schematic (some errors) but it shows the power to Pin 18/55 coming through the 5 Amp fuse from the "30" constant power bus.

illgetyou22

UrS4boy: I did check this before and i was getting power to the red fuse holder using a test light ill check if im getting 12v or not also this power should be on even if the ignition is off correct? Also if i am getting 12v volts to the red fuse hold were does the white wire with the black stripe run straight to the ecu to pin 18?





scarman: Im using the vw scan tool(dealer tool) with the adapter cable so it should read (ive used it on obd1 corrados) also when i hook up to the port the scan tools battery light goes on so the port has power.There is no one near me with another urs4 that i know this would make it easier.

UrS4boy

The white wire with the black stripe that leaves the red fuse holder likely goes less than a foot where it enters into the wire bundle that terminates at the T55 connector, as shown in the photo below. You should be able to put one end of a multimeter set to Ohms in the output side of the red fuse holder (the side attached to the white/black wire) and the other end in Pin 18 of the T55 connector and get continuity. IF not, (which I suspect is the problem), you need to find out where/why the wire or the connection to the red fuse holder or the T55 is broken (or the wire is broken)

illgetyou22

Ok cool that's exactly what i wanted to know im going to do this in the next couple days ill let you guys the outcome and thanks again for all the help