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Michael, ASE Certified Technician
Category: Volvo
Satisfied Customers: 905
Experience:  Volvo Master technician, ASE Master, EPA 608&609 certified
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98 v70xc wont start...occasional - when engine was warm

Customer Question

'98 V70XC won't start. At first, it was occasional - when engine was warm. When the engine got completely cold it would start again. Now it won't start at all. No spark coming out of the coil. There is 12V in the primary circuit coming in and out of the coil.
Submitted: 8 years ago.
Category: Volvo
Expert:  Michael replied 8 years ago.

Check to see if the fuel injectors pulse.
If they do not. the problem is most likely the crank sensor.

If they do let me know and we can do some more checks.
Customer: replied 8 years ago.
How do I check if the fuel injectors pulse?
Expert:  Michael replied 8 years ago.
The best way is to install a noid light in place of an injector.
You can listen for the injectors to click.
Or you can connect a voltmeter to an injector connector. It should read voltage when the ecm grounds the circuit.
Customer: replied 8 years ago.
I bought a noid light and yes, the injectors receive electrical pulses.
Customer: replied 8 years ago.
The noid light shows me that injectors are getting pulsed. Does it mean that the crank sensor is working? What would be the next step?
Expert:  Michael replied 8 years ago.
If the injectors are getting a pulse than the computer sees the engine turning.
Check the signal wire to the coil connector. See if it is getting a pulse. I beleive it is the yellow wire.
Customer: replied 8 years ago.
I disconnected the red and blue wires from the coil. With the ignition on, I get a steady noid light between the red and ground; no light between red and blue. No change when cranking - still steady light. What does that mean? What would be the next step?
Expert:  Michael replied 8 years ago.
The wires you are checking sound to be right on the coil.
The coil is mounted on a bracket with a connector. This is where you need to check.

Here is the part of the wiring diagram showing the coil 4/44.

Check for a signal from the ECM on the yellow wire at terminal 4.
If there is a signal here the transistor part of the coil is faulty.
Customer: replied 8 years ago.

There is no signal on terminal 4. There is only a steady signal on terminal 3.

Expert:  Michael replied 8 years ago.
Terminal 3 should be battery power.

Terminal 4 is connected to the yellow wire. It should be a pulsing signal.
If you have no signal here I would go back to the ecm and see if you have a signal there.

If the ecm is grounding the injectors it should signal the coil.
Customer: replied 8 years ago.
Where do I find the ECM (is this Engine Control Module?/computer)
Expert:  Michael replied 8 years ago.
The ECM is in the box behind the right headlamp.
It will be the one close to the fender.
With the ECM out use an ohmeter to check the wire for an open or a short.
Customer: replied 8 years ago.

Not sure if I'm doing it correctly... I pulled out the ECM and checked for continuity between terminal #11 in the ECM socket and terminal #4 in the connector that I unplugged from the ignition coil bracket. There's no connection (open).


Does that indicate that the wire running from the ECM to the coil is broken? If so, what would be the best fix?

Expert:  Michael replied 8 years ago.
If you have the correct terminals, yes that would indicate an open.
I would run a new wire connecting the two.
Connect a temporary jumper wire to confirm this first before you install one all neat and tidy.
Customer: replied 8 years ago.

I hooked up a wire to terminal #11 on the ECM module that's close to the fender and did not get any signal.

I then traced the wire from terminal #4 on the ignition coil all the way to to the socket for... the other ECM, not the one close to fender but the one away from the fender. That wire is OK and so there's no signal coming out of ECM.

I guess the next step would be to check if the ECM is getting an input signal from the pick-up coil (?) or some other sensor (?). Is item 4/46 on th electrical diagram you sent me the ECM? Which wire on the diagram provides the timing signal to the ECM that triggers the pulse to the coil?

Can you send me some kind of legend for the schematic that would tell me what the different devices are? Is the schematic you sent me complete?