My daughter's 1993 940 Non-turbo has the dreaded code 143 for "knock sensor signal absent or faulty." After clearing the code the light comes back on within two days. Checked the normal items listed here to no avail. Replaced the knock sensor with a new one from FCP Groton. Torqued the sensor bolt to 8 lb-ft with blue locktite. Cleaned the knock sensor connector with Deoxit. Pulled all the engine wire harness connectors at the firewall on the driver and passenger sides and cleaned with Deoxit. Keeps tripping code 143 ever couple of days.

Considering relocating the knock sensor wire harness away from the alternator wire harness but is this really a possible solution?

I think this explains why the previous owner pulled the check engine bulb from the dash.

Thanks for any advice.

Rob Ippolito
93 940 Volvo
90 740 Volvo GL Wagon

UPDATE - Knock sensor trouble light fixed. One of two things fixed it:

1. Changed the plugs from old copper core to Bosch Platinum. The old plugs looked okay and car appeared to run fine. Maybe the engine was missing or knocking slightly and we didn't notice.

OR

2. The Fuel Injection/Radio Suppression Relay went bad and caused an intermittent warm non-start and stall. Replaced the relay. The bad relay was possiblily causing an intermittent lean condition and knock.

Anyway it's fixed and thought I'd share the fix.

Rob

hi rob,
has your 1-4-3 sensor code remained off?

my 94 940 trips them, too. also, my car starts fine, but after a few minutes, it starts running rough. at operating temperature, it runs fine again.

i notice when it's dry, i don't seem to have this problem.

thanks,
byron golden
86 245
92 245
94 940

I had this problem on my 1993 945 for years. Finally solved it by running a new, shielded wire from the sensor to the ignition computer plug, and routing it well away from other wires that could be corrupting the signal.

Got the wire from an electronics supply store, it has 2 conductors plus the shielding. Bought new connector clips from the dealer for the ends going into the ICU plug, and got a used sensor-end connector from the junkyard. I left the original wiring in place, just tucked out of the way. Grounded the shielding at both ends of the new wire.

I have not had a knock sensor error code since doing this over a year ago.

john
--
1989 245 241K / 1993 945 127K

john,
many thanks for your reply. i agree with j.e. (spook). as often as this issue has risen, this would be a go for the FAQ.

questions:

a. how did you fit the new wiring to the 10 or 11-pin bendix connector plug with all the other wiring wrapped up?

b. did you pick up a 10-pin bendix connector from the junk yard or just took off the tape and swapped out the original knock sensor pins out of the plug and put the new, shielded wire connections in its place?

c. also, did you have hesitation problems after a few minutes, as many of us have had with the rex/regina system?

d. if so, did this seem to fix that problem too?


so, to my understanding, you did the following.
1. used 2 wires shielded with connectors
2. ran them from the knock sensor,
3. spliced to a knock sensor connector (i have a spare one too).
4. ran in the engine bay through the firewall away from other possible sources of interference
5. to the icu bendix, inside the car, and grounded the shielding on both ends.
6. using volvo connectors same as the other connectors to the icu.
7. you kept the original knock sensor connector intact, uncut.


i think that would be best which would one can avoid unraveling that wiring loom.

i would have tried to connect it to the gray connector, but i didn't think that the interference may be coming from the interior.

i'll get this done for sure.

thanks,
byron

My goal was to eliminate as many sources of electrical interference as possible, so I ran new cable the entire way from sensor to ICU. This may have been overkill, but maybe it wasn't. I'd been able to make the error code go away from months at a time by cleaning the connectors in the big gray plug at the firewall, so I felt removing that obvious weak point was wise. The idea of cutting open the factory harness and trying to fish out the original knock sensor wire to re-route it seemed like inviting catastrophe.

The wire I used was Belden 18AWG 2 Conductor Shielded Twisted Pair Cable, which I ordered from Altex.com. Quality stuff.

Disconnect the plug from the ICU, then take the back cover off the plug. Once things are opened up, you can remove individual wires with their connectors from the plug body using a tiny screwdriver blade. They are very delicate, and I forget the exact technique, but it is indeed possible to remove them without damage. I folded them back and bound them to the harness with a few wraps of electrical tape. Then once the new wire was fished through the firewall, I attached the 2 new connectors (bought from the dealer, don't know the part #) and seated them in the plug body. Attached a short lead of normal wire to the shielding and ran it over to the ground point in the footwell--plenty of spare terminals there.

Under the hood, I attached the new cable connectors to a used knock sensor connector savaged from a junkyard. I did not want to hack up the existing wiring harness. The old plug got a thick coat of dielectric grease over the contacts and was then ziptied up and out of the way. Should also run a new ground wire from the shielding of the new cable to the injector/coil ground point on the intake manifold.

I have had the hesitation problem a couple of times in the years I've owned the car, but it was always so rare that I cannot say whether it was also solved by this wire re-routing. It hasn't happened since I did this, though.

John
--
1989 245 241K / 1993 945 127K

john,
from your tip, i rewired my knock sensor with new contacts and the belden wire. luckily, we have an altex store here in town. new contacts to the sensor are the same ones used for the injectors, so no problem there, and i bought volvo repair wires with contacts for the wires going to the bendix ignition control unit.

it's only been a week, but i notice immediately it's running a lot smoother, no codes thrown, and no rough idle in the mornings.

while doing the repair, i noticed the original green wire near the sensor end is brittle and had split, probably causing the short (grounding out) and throwing the codes. the split probably became worse when i and others handled the connector more often, trying to make sure of a good connection. the more the codes were thrown, the more the original wire was handled, the worse the problem became.

humid mornings caused idle problems, too. but all is fixed.

yes, i agree this fix should be a write up in the faq.

regards,
byron golden
86 245
92 245
94 940

Dear Dinomartino,

Hope you're well.

Your further write-up should be added to the FAQs.

Thank You!!!

Yours faithfully,

Spook

Dear dinomartino,

Hope you're well. Your fix should be in the FAQs. A lasting solution to a persistent problem should be where it can easily be found.

Hope this helps.

Yours faithfully,

Spook

Give it some time before declaring it fixed. My 1993 940 has the same chronic fault. I've been able to significantly reduce it, but every once in a while (always in summer) I'll start it up and the system is audibly on full retard, and a short time later on comes the light with a 1-4-3 code.

I have contemplated installing a new (shielded) wire directly from knock sensor to the main connector on the REX, and taking the existing wire out of service. Opening up the harness and trying to separate the wires is clearly madness.

john
--
1989 245 233K / 1993 945 127K