• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

1994 940 turbo won't shut off when radio suppression relay is plugged in

herbiedriver

herbiedriver

New member
Joined
Sep 20, 2022
Location
Boulder, CO
Strange gremlins happening... 94 B230FT threw a 121 code, cleaned the MAF, cleared the code no problem. Notice and reattached the loose radio suppression relay to the fender, started the car and it wouldn't shut off with the key.

Removed the relay and the car starts and shuts off... what the heck?!

Tested the relay, put 12v to it, clicks on and off...

What to look at next?
 
Isn't the radio suppression relay right next to the 5V injector power relay? Could they be swapped, or impossible (different plug)?

Sold my wiring diagrams for the late 9 series......but troubleshooting from the diagram will solve your mystery.
 
I too have a 1994 Volvo 940 turbo that had starting and stalling issues; got a New Standalone and replacing All Ignition and Fuel related wiring...Upon removal, I discovered Plenty of Corrossion and Burnt/Heated wiring in many areas of the loom....I would peel back the Loom & wire sheathing and get a better look-see...
 
herbiedriver said:
Notice and reattached the loose radio suppression relay to the fender, started the car and it wouldn't shut off with the key.

Removed the relay and the car starts and shuts off... what the heck?!

Tested the relay, put 12v to it, clicks on and off...
Click to expand...

Was the relay plugged in before?
Are you the first owner?
If no, any chance a previous owner "bypassed" the relay?
The relay clicks (power to pins 1+2), but do the output pins (3+4) connect and disconnect with the clicks?

herbiedriver said:
Isn't the radio suppression relay right next to the 5V injector power relay? Could they be swapped, or impossible (different plug)?
Click to expand...
As far as I know, the RSR *is* the injector power supply relay.

Looks like when the key is on, power comes from ignition switch 15R to the distbibution box, then out blue to ECU pin 35. Fuse 1 powers main FI relay pin 3. ECU grounds 21 red, which closes half the main relay, powering its own pin 1. Power goes out blue/yellow to pin 6 (which allows pin 2 yellow/black to close the other half, turning on the fuel pumps via 5 pink), and continues to RSR pin 2, turnng it on and allowing battery power 4 red to the injectors on 3 grey, and also the coil on blue. Simple, yes?

If the RSR relay is stuck on, or there's some other unknown problem, someone may have "bypassed" the RSR incorrectly, maybe directly wired to somewhere it shouldn't be.

Here's a nice diagram:

940vin87.gif
 
Thank you for the diagram! The relay was plugged in the entire time I have owned it. Started out as a Check Engine and a wonky idle. Code said MAF (121) Took out the MAF, cleaned it with CRC Mass Air flow cleaner, let it dry, reinstalled, started car, CEL still on but ran a bit better. Cleared code, took out the crank position sensor, wires look good, reinstalled, and moved the RSR relay to see why it wasn't attached to the hanger, plastic hanger is broken. Started car, and idled ok, went to turn off, and key moves all the way off, but car runs all lights on dash. Had to pop it into gear to get it to shut down.
Disconnect battery, removed ignition switch, tested good, reinstalled, started, wouldn't shut off.

Ran the diagnostic test through OBD, all good with the exception of the SRS relay, it never clicked, couldn't shut car off again, disconnect relay, all is good...

I cannot figure this out!
 
Something if funky about the ignition switch- you shouldn't have any dash lights with the key off. Any modified wiring?
 
PCH said:
Something if funky about the ignition switch- you shouldn't have any dash lights with the key off. Any modified wiring?
Click to expand...
It only happens when the RSR is plugged in. It just happened today... driving me batty! I can't find any modified wiring, all relays are in place, no fuses blown. Like I said, it started with a CEL, code 121
 
Without working RSR relay the car should not run at all. Are you saying it starts and runs with it unplugged?
 
Almost sounds like the RSR is shorting something internally. I.e the battery power coming in on pin 4 is getting shorted to the control circuit, latching itself on and possibly back-feeding other circuits.

Or like boxtoy implied above, that you have shorts in the wiring harness somewhere... But in that case I wouldn't expect them to come and go by just manipulating the relay unless you're really wiggling the wiring around while you're at it.
 
Look for the alternative source of battery voltage at the coil and the injectors. Plugged in and working RSR is the only thing that should make "+" present. Hope you are good with the test light and the wiring diagram.
 
Spent most of the morning trying to troubleshoot this stupid relay issue. Nothing. Car runs, drives, stops and starts with the RSR relay disconnected.

Plug the relay in, turn the key to II and all the dash lights come on, everything energizes and then stays on. Pull the key out and it all stays as if the key is still in the ignition. I unplugged every circuit (I think) that the RSR powers trying to nail down where the issue may be, MAF, Knock Sensor, IAC, Power Amp, Injector Resistors, fuel pumps, O2 sensor, temp sensors, nothing. The 3 things that will shut the power down are removing the fuel injection relay (which tested good), the #1 fuse, or remove the RSR relay.

Searched the wiring loom for any obvious misdeeds by previous owners, and found nothing, also no indication of burnt or torn insulation.

I am at a loss
 
It is possible that you have a failed ignition switch.

The ECM and the coil would need to stay powered for the engine to stay running.

All you are doing by pulling the relay is cutting power to the injectors and stalling out the engine. You are looking in the wrong direction.
 
ZVOLV said:
It is possible that you have a failed ignition switch.

The ECM and the coil would need to stay powered for the engine to stay running.

All you are doing by pulling the relay is cutting power to the injectors and stalling out the engine. You are looking in the wrong direction.
Click to expand...
I pulled the switch today again, tested it on the bench fed it 12v and tested all outs, nothing 'stuck' and all turned on and off as they should. I feel like I am going crazy. But hey, I am almost expert level at removing the switch now...
 
Ok, I looked at that diagram pictured above. I guess the relay also powers the coil. I thought it only powered the injectors.

At this point, I would be poking around with a test lamp.
 
Last edited:
Unplug and remove the RSR from the car and measure resistance between #4 and #3 (That's where Red and Grey wires plug in). If there is a small resistance of just couple Ohms then your relay is closed without being powered. You may want to measure in few positions- with relay upside down, on it's side, the way it sits on the fender. That's the first step. Leave the relay out.

Then with the probe connected to Ground turn the key On and touch Grey wire at the RSR plug. If the probe lights up then your wiring has been modified with the jumper between Ignition/Start Power and Coil/Injectors Positive.
 
Ok so looking again at the diagram, the Main Relay controls the RSR relay.

You need to get the test lamp out and do some circuit chasing. If you have power on the blue/yellow to the MAF sensor, the RSR is commanded on by that circuit. So go poke a test lamp into blue/yellow at the MAF, key off, and report back. At which point you would need to figure out what is turning the main relay on. THAT relay could be shorted internally and cause this issue. It powers up the whole chingus.
 
ZVOLV said:
Ok so looking again at the diagram, the Main Relay controls the RSR relay.

You need to get the test lamp out and do some circuit chasing. If you have power on the blue/yellow to the MAF sensor, the RSR is commanded on by that circuit. So go poke a test lamp into blue/yellow at the MAF, key off, and report back. At which point you would need to figure out what is turning the main relay on. THAT relay could be shorted internally and cause this issue. It powers up the whole chingus.
Click to expand...
Are you referring to the Fuel Injection relay? If so, I have already removed that and tested that as well. I am scouring the wiring diagrams to find a Main Relay
 
Here's a simple test. With the RSR relay removed, turn on the key but don't start it. Do you have +12v on the ignition coil tabs? If so, something is back-feeding voltage (aka bypassing the RSR) to power ignition/injectors. I think the fuel pump may be back powered too.
 
You must log in or register to reply here.
Back
Top