850 N/A code 143

[Teddy1975]

I had the engine in my 1996 850 N/A replaced with another B5202FS (10 valve). It's done 123K miles and has good compression even after having sat for an unknown amount of time. It starts smoothly even in damp/cold weather and has "all" the power that can be expected of a 126 bhp N/A engine, which isn't much of course, but is enough for me. PCV, waterpump and the belts were done at the time of the swap, just two months ago.

But, the check engine light is on, and the only error is 1-4-3 "(front) knock sensor signal missing or sensor defective". I spoke to the guy who did the engine swap and he says the knock sensor is fine, and I trust his judgement as he has been working with Volvo cars since 1972, since before I was born. I can reset the check engine light and it'll stay off until the RPMs go above 4500 in 3rd gear, at which point it'll go back on until I disconnect the battery. There are no strange sounds nor vibrations from the engine, at least none that I can tell from behind the wheel.

I guess I could ask the guy who did the engine swap to figure out what the problem is, but before I do that and maybe end up having to pay for far too many work hours for my wallet, I thought I'd ask here for any hints as to what can possibly trigger a 143 code? I'm able to do some diagnostics on my own with a volt/ohm meter.

My car is up for inspection in about eight weeks time and it needs to have a working check engine light and without it being lit otherwise I'd be happy to simply ignore it as the car does drive very well now, regardless of the code.

Thanks,
Teddy

[jtp]

It might be the connectors, this thread is good viewtopic.php?t=37656

[scot850]

Check what else is on the same circuit as the knock sensor. Been a while but I think I recall that there are other sensors on the circuit but don't recall what. Maybe the barometric sensor by the RH hood lock? I had an issue on a 93 850 GLT maybe 10 years ago and the code was for the knock sensor but it turned out to be something else on the circuit.

How recent are the spark plug cables and distributor cap/rotor arm and spark plugs?

Neil.

[RickHaleParker]

1-4-3 means the ECM is not hearing the KS, it does not mean a fault in the KS has been detected, however a fault in the KS could be the reason the ECM is not hearing the KS.

Check the grounds and other wiring to the front KS, it maybe a communication problem or a power supply problem.

DTC information1-4-3 and 4-3-3

S151507 Condition

• If there is no KS signal with the engine warm and the throttle open, and with the pressure sensor signal greater than 750 mbar and the engine speed around 3100 rpm, DTCs 1-4-3 or 4-3-3 are recorded.

Substitute value

• The control unit retards the ignition in the cylinders connected to the KS whose signal is missing.

Possible source

• Open-circuit in ground lead.

Fault symptom

• Engine may falter.

[Teddy1975]

• If there is no KS signal with the engine warm and the throttle open, and with the pressure sensor signal greater than 750 mbar and the engine speed around 3100 rpm, DTCs 1-4-3 or 4-3-3 are recorded.

Substitute value

• The control unit retards the ignition in the cylinders connected to the KS whose signal is missing.

Possible source

• Open-circuit in ground lead.

Fault symptom

• Engine may falter.

That is pretty bang on what happens, though I haven't noticed any faltering of the engine.

It might be the connectors, this thread is good viewtopic.php?t=37656

I'll have a look at the connectors, hopefully I can find a way to getting to them without having to remove the intake manifold, I've done that so many times in the driveway it isn't funny anymore.

How recent are the spark plug cables and distributor cap/rotor arm and spark plugs?

All are four months old with less than 1k miles on them as I put them on the old engine to troubleshoot a very extreme lack of power. The lack of power turned out to be a burnt exhaust valve and a broken exhaust manifold pinbolt stuck in the block, hence the replacement. The pinbolt was impossible to drill out with the engine still in the car, and since a replacement engine wasn't expensive at all, I decided to go for that.

I put in Bougicord (sp?) cables, Bosch rotor and cap, Volvo 3 prong plugs and they were transfered from the old to the newer engine during the swap.

When I got the car back, it had code 122 and 143, which was believed to be due to a stuffed up O2 sensor. The 122 cleared itself by adding additives to the fuel and I was happy to drive with an error free car that ran beautifully, only to get slapped in the face on the first overtake I did.

Just to be clear, 143 isn't set because of knocks/vibration from inside the engine, it's only set because of lack of communication with it? I'm only running the car on 95 octane fuel, as the owner's manual recommends.

/Teddy

[RickHaleParker]

When I got the car back, it had code 122 and 143, which was believed to be due to a stuffed up O2 sensor.

DTC information1-2-2

S151514 Condition
DTC 1-2-2 is set if the signal from the air temperature sensor corresponds to a temperature below
-40°C (5V) or above 120°C (0V).

Substitute value

• If the water temperature is below 20°C, the control module assumes the air temperature is the same as the water temperature; otherwise, it takes the air temperature to be 20°C.

Possible source

• Signal lead shorted to ground or another supply lead.
  Open-circuit in signal or ground leads.
  Faulty air temperature sensor.

Fault symptoms

• No noticeable symptoms.

Just to be clear, 143 isn't set because of knocks/vibration from inside the engine, it's only set because of lack of communication with it?

Correct, the ECU expects to hear from the KS knocking or no knocking. This is to insure the KS is operational if it is needed.
This is proactive preventive maintenance. If the KS is not operational and the engine starts knocking, you would acquire some serious damage because the ECU would not know it needs to derate the engine and stop the knocking. When the ECU does not hear the KS, it goes ahead and retards the engine to insure this does not happen. Right now your engine it is running with retarded front cylinders on 1,2 & 3 . When the 1-4-3 is dealt with, your engine will run better.

[Teddy1975]

The 1-2-2 is gone, so it's just the 1-4-3. The more I think about it, the more likely it seems that it's a bad ground lead since the check engine light came on when the engine was warm and at WOT.

I'm going to talk to the indy mech who installed the engine and see if he can be talked into fixing it without charging an arm and a leg. Obviously he didn't do the job right the first time.

Thanks for all the invaluable info, guys. I'm going to leave the topic unanswered for now until the problem is fixed and follow up with what was done to fix it.

[RickHaleParker]

You might want to print out my write up and take it to the mechanic. That way your have facts, not an empty hand to play with.

[Teddy1975]

You might want to print out my write up and take it to the mechanic. That way your have facts, not an empty hand to play with.

Oh yes. I sent him a mail today as I need him to look at some other issues anyway. Asked him if he could fix the code for free as it clearly was there when I left the shop after his mech had made the engine swap. If not, I'll have to find another indy mech who I can trust my car with.

[RickHaleParker]

If not, I'll have to find another indy mech who I can trust my car with.

I don't know what the statistics are in Denmark but, here in the U.S., at random you got a 50/50 chance of getting ripped due to incompetence or fraud. Once you located a honest and competent mechanic stick to him, pay him what he is worth and take all your work to him, that way he knows the history of your car. Knowing the history of a car will cut down on incorrect dianostics, save time and money.