Good evening,
I am newly registered on this forum and still finding my way around. This is my first post, so greetings to you all.


I have owned and serviced/repaired my Volvo's for many years with a series of 240's followed recently by a V40, which quite frankly seemed a good idea but is too small.


Very recently I jumped at the opportunity to buy a 1992 model 240 Torslanda 2.0 Estate ( 167000 miles on the clock) at a good price because it had failed its MOT on emissions and been off the road for about a year. Despite being a little tatty with lots of small jobs needing doing, once cleaned up and worked on it's in good condition.

It is quite a retro style vehicle and has no OBDII and very little other electrical operated equipment or systems that can cause problems.


When you lift the bonnet everything is easily identifiable and relatively accessible, making it a joy to work on despite plastic fittings that break easily and rusted nuts/bolts.


I have enjoyed working on this and already done quite a few repairs, improvising in certain areas and doing things that people tell you can't be done outside of a workshop.


My next job is to replace the exhaust system and Lambda oxygen sensor (I believe this is the likely cause of emission problem) which as I don't want to buy the wrong goodies brings me to my questions.


1. The existing Lambda sensor is mounted into the Cat, which I assume was the standard mounting point for this model, but bearing in mind the age of the car I want to be sure this is correct. Can anyone confirm this please?

2. There is also a blanked off mounting point in the upstream pipe. I assume this was to make provision for any models fitted with double sensors and nothing to concern myself over?


3. Someone has replaced this Lambda sensor with a cheap generic version which obviously hasn't worked as the warning light is still on. Can anyone help with the correct/preferred Lambda sensor (Bosch?), Model No, etc


All advice would be greatly appreciated.
Pete

 

a standard narrowband bosch 3-wire sensor, as used in countless european cars in the early/mid 90s should fit fine. 2 wires are for the heater, the 3rd wire is the shielded signal wire. a real volvo one would have the right connector so you don't have to splice, so does a Bosch 13034, like PartInformation

 

Thanks Pierce.


Just a brief update FYI.


Checking vehicle MOT test paperwork it had previously failed both cold and hot emissions test. I think previous owner then replaced Lambda sensor as this looks new and it subsequently passed cold test but still failed hot.


Upstream pipe had obviously been recently replaced with no significant corrosion so have ordered cat and new Bosch Lambda sensor to be sure.


Still awaiting parts but started loosening/removing downstream pipe/boxes in preparation for replacement.
Had to move car during this and interestingly found warning light had gone off.
Suspect lower downstream pressure resulted in increased gas flow through cat, possibly caused by partial internal collapse/blockage.


I will give further feedback after parts arrive/installed.
Thanks again,


Pete

 

Eventually found time to do some more on this so here is update.
Changed cat and Lambda but warning light still on.
However, had an epiphany moment and discovered LED diagnostic box which I had no idea existed.
This had a number of memorised alarms but after reset it only identifies an engine coolant sensor problem, so replaced it (not expensive although a pig to access) but no change.
Then checked wiring and plug/socket connectors (using digital meter) which appear good with continuity from section to section and end to end (one side of sensor plug to ECU plug mounted in passenger compartment on RHS of firewall; other side of sensor plug to a Bosch control unit mounted in passenger compartment on LHS of firewall which I assume is for injection/ignition control but can't identify it referenced anywhere).
Even bypassed wiring (bit of a Heath Robinson lash up with crocodile clips, etc, but good end to end continuity) with no improvement.
Then measured cold and hot sensor resistances which seem OK (cold about 2600 Ohm at ambient 26 degrees F and hot 270 Ohm at about 180 degrees F).
During this process disconnected sensor plug with engine running and it does not affect anything (engine continues running at same speed, warning light still on, same LED readout) so obviously there is an open circuit somewhere.
My final check of the day was to measure voltage either side of sensor. This was just under 6v which on a 12 v system doesn't seem right. If too low it could be the problem, but as I don't have a wiring schematic can't be sure!
Gave up for the day and retired to put on my thinking cap.
My next actions will be to try to access a wiring schematic and to remove the dashboard facia panels to get access to the concealed wiring and check that there is nothing happening here (intermediate plugs, immobiliser/ignition switches, etc).
As the problem has changed from where I started I will now begin a new thread on this, but any further input still much appreciated.

 

According to my Haynes manual, the resistance measurements you made to the ECT are within spec (250-300 ohms hot, 2100-2900 ohms cold). I assume you took these measurements directly at the sensor (wires disconnected). I would take the same measurements from the ECU side to see if the readings are the same when including the wiring in the measurement. If you get the same numbers as measured at the ECU, I would say that you have eliminated the ECT as the issue.

From the sounds of it, your ECU may be running in open loop mode - meaning it is using a predefined fuel map instead of relying on feedback from the oxygen sensor and AMM to set the mixture. Normally, when the engine is cold (as measured by the ECT), the ECU runs in open loop mode till a certain temperature is reached. Only then will it run in normal mode. I would verify all the wiring to the oxygen sensor and the AMM as well. Also, verify that the correct AMM is installed for your car.

 

so this is an Bosch LH 2.4 fuel injection system? We never got the 2.0 over here and often euro cars have different setups than US...

the ECU is on the right side of the right footwell, behind the plastic panel thats just forward of the right front door hinges. the best place to measure the CTS resistance is at this connector, if you unplug it and shine a small bright flashlight in there you can read the pin numbers molded into the plastic. pin 13 is the coolant sensor, and pin 5 is the signal ground. the other half of the coolant sensor goes to the ICU (EZK116 ignition control unit), which is mounted on the firewall not that far from the ECU, its pin 2 and pin 20 is ground.

 

Have further tested circuits and components but problem remains, with diagnostic leds reporting Engine Coolant Sensor problem and I believe engine running in open loop mode, now compounded with unable to start.


However, traced start problem to fuel pump not running so checked fuses, linked across fuse terminals 4 & 6 and pump starts OK so will replace fuel pump relay.



Engine Coolant Sensor.
Open circuit resistance. 3400 Ohm Cold and 320 Hot.
Voltage at ECS. Have measured very different levels as though something else switching in or connecting in circuit. At cold has been 6v, 3v and 0.2v where it now seems stuck, with no change at hot running.
Checked continuity on all wiring and intermediate plugs, removed ECU socket cover and back probed connections 13 (coolant sensor) to 5 (signal earth) but still only 0.2v, so suspect ECU.



However reluctant to replace at high cost unless sure and I can only get it professionally checked by sending away which is also quite expensive and with cost of repair would most likely be more sensible to buy a new one.
Basically I don't want to risk still having the same problem afterwards, and my main concern is whether there could be anything else in this circuit (ECU to ECS) parallel connected that could be affecting/dragging down the voltage.



Any ideas for further checking would be greatly appreciated.


PS. Have also checked MAF sensor (pins 2 and 3) and get about 2.5v at idle immediately responding/increasing on revving engine.

 

I have not seen any specs as to what the voltage measured across the coolant temperature sensor. All tests specify to check the resistance of the sensor at different temps. The values you are reading seem within spec. Did you measure the resistance of the coolant temperature sensor by probing it from the ECU connector? Your post seems to indicate you took voltage measurements at the ECU.

 

ECS resistance readings were open circuit, i.e. directly across the disconnected sensor and cross checked at the unplugged ECU end with it reconnected .
All the continuity checks on intermediate wiring/plug & socket connectors were open circuit.


Voltage checks were done at various points from ECU output to ECS input.
After it dropped to 0.2v no apparent difference whether sensor connected or disconnected.

 

I'm trying to understand what voltage measurements you are taking but somehow just don't get it. I would take a resistance measurement from the ECU connector (ECU disconnected) with the coolant temp sensor in-circuit. Basically, this is what the ECU sees. If it doesn't match the measurement taken directly at the sensor, then there is something in the circuit causing the issue.

 

OK, let's separate resistance and voltage.


Resistance. As previously stated the ECS was tested open circuit across disconnected sensor and again (with the sensor reconnected) across disconnected ECU plug, both readings effectively identical and within spec.
This would suggest sensor and circuit to ECU OK and my only uncertainty is whether anything else comes into play when system powered up through ECU, recognising that one of the ECS connections goes to the ECU (pin13) and the other to the ICU (pin 20).


Voltage. The sensor connects to the ECU which applies a reference voltage to it which I understand should be a nominal 5v, This will obviously drop across the ECS resistance, I believe to around 3v + when cold (ECS resistance high) and +/- 1v when hot (ECS resistance low).
I currently seem to be getting only 0.2v at all times, which suggests to me either that the ECU is faulty and the engine is running in cold start open loop mode or that something else comes into play when switched on dragging the voltage down.
I can only measure ECU outputs by back probing into connected plug, as disconnecting plug also disconnects its power supply.


I hope this helps clarify understanding.

 

Where are you getting these voltage specs? Volvo green book? Bentley manual?

The FAQ at brickboard lists the voltages as follows:



The resistance values between ECU pins 13 and 5, or between each of the pins on the sensor and ground, are (by eye from the chart):

32F (0C)-- about 6000 ohms within a range of +/- 10%
68F(20C) -- about 2300 ohms
104F(40C) -- about 1300 ohms
140F(60C) -- about 600 ohms
176F(80C) -- about 300 ohms
212F -- about 190 ohms

[Response: Steve Ringlee] ECT resistance cold for LH2.4 systems should be around 6k ohms at 32 degrees F (0 deg C), 2300-2700 ohms at 68 degrees F (20 C), and 200 at 212 F (100 C). However, try checking your ECT wiring: Between pins 13 and 5 at the LH ECU (with sensor DISconnected) resistance should be infinite. Voltage with the ignition ON and sensor connected, measured between pins 13 and 5, should be:

0 C=around 3 volts +/-.5v
20C=around 2 volts +/- .5v
100C=around .3 volt +/- .1v

If these aren't correct, check the connections in the ECT wiring harness. Check engine ground connections at the intake manifold. If the voltage is zero, your ECU is at fault.

 

Thanks for this input, much appreciated.
I am reasonably confident that cold and hot sensor resistances are indicatively OK, with no loss of continuity through wiring/plug & sockets (2600 Ohm cold and 270 Ohm hot) measured at disconnected sensor and cross checked (with the sensor reconnected) at disconnected end of wiring plug connection into ECU.


Quite frankly I have lost sight of where I got my original voltage levels from but in trying to find Volvo data checked various sources. This is a thermistor type sensor which seems to operate on a reference (open circuit) level of 5v from the ECU. When connected this relies on the voltage drop across the thermistor to calculate coolant temperature and adjust control settings as this changes, which all seems to tie in with the voltage/temp levels quoted. Not Hi Tech but quite effective.

I still have a little concern whether something else comes into play when powered up, recognising that the ECS connections go to both the ECU and the ICU, but haven't been able to trace anything obvious in these circuits.


I haven't measured internal resistance across ECU pins 13-5 as I was a little concerned about injecting a test input voltage without knowing the internal circuitry was adequately interfaced, but an infinite resistance suggests this shouldn't be a problem so will check further this weekend.


Irrespective, as I seem to be getting a reference level of only 0.2v at all running conditions (hot/cold, open/closed circuit), measured across the sensor and cross checked between pin 13 to pin 5, it looks like an ECU problem, and I will most likely have to bite the bullet and either get it repaired or replaced.



I have checked earth connections throughout as this was one of my first concerns, but will double check intake manifold earth connection to be sure, although with the low voltage feed from the ECU I think it most unlikely.


Once again many thanks for your input and I will update when I have further progress to report.

 

My apologies for long delay in providing this update.


Cutting a long story short I have thoroughly checked every sensor/signal level (and replaced most of them) and all wiring/earth continuity circuits.


A couple of hard knock lessons learned along the way.


The Flywheel housing mounted Position Sensor looked very old with its wiring insulation and shield in a sorry state.
In trying to remove found it was fused into its mounting bracket which broke, and as impossible to exchange in situ had to drop the gearbox to replace.


Having checked and replaced almost everything except the engine and ECU/ICU with no success (engine still not running smoothly, warning light still on and diagnostics still showing Engine Coolant Sensor problem - in other words exactly where I started) I retired sulking to collect my thoughts and generate enough energy/enthusiasm to continue.


However nothing has beaten me before, so after much consideration the only thing I could come up with was whether problem could be due to using generic products.


I decided to return to the beginning of this sorry tale of woe and bought a genuine Volvo Engine Coolant Sensor, which had to be brought in from Europe at 4 times the cost of the generic version.
This seemed visually identical, and resistance checks were similar so I replaced it with some trepidation, started the engine, and - it ran perfectly!


I don't know what the difference in sensors is and have no intention of unnecessarily further playing with them to find out.
Suffice it to say it sailed through the MOT with flying colours.


On a positive note I have now thoroughly checked everything, replaced most sensors and various joints/bearings, fitted new discs/brake pads/exhaust system/tyres, and should have a reliable runner for many years.
Sincere thanks to everyone for their salutary advice and guidance.
Best Regards,


John