S40 V40: Normal fuel pressure while engine is running

[ww1dm1]

Originally Posted by KBB

Short term fuel trim are the ones to look at 7%LTFT is not an issue.

run car at idle and look at STFT values if they are in the positive area raise RPM up 2000 and hold note STFT values and raise again to 3000 RPM and hold. If the STFT values are heavily positive at idle but then roll back to a lesser value as the engine is loaded then I would be looking for a vacuum leak.

If STFT is in the negative at idle and then goes heavily positive under load then possible MAF sensor contamination affecting the calibration of the sensor, I usually follow this one up with a volumetric efficiency test to confirm MAF diagnosis and a wide open throttle test with a scope monitoring 02 sensor an MAF signal voltage should reach 4.2v.

If STFT at idle is good but going heavily positive under load and MAF voltage has proven good then even if fuel pressure is good a volume and flow test is needed. this also means checking for voltage drop on the pumps supply and ground. I had a pump that displayed specified pressure at idle and load, the pump had a 2v drop on the ground side which reduced its volume delivery by 40%. Dose you scan took have live data and graphing capability?

My front oxygen sensor voltage is constantly zero at idle, which as I understand means a positive STFT. I believe that should keep increasing the LTFT until voltage oscillation occurs. If I recall correctly, when I push the throttle the voltage shoots up to 1V and immediately goes back to zero again. I'll have to check again, this is some good information. I'm using ELM327, live data is available for the oxygen sensors.

[KBB]

If your O2 sensor is pegging low at idle you need to check on the scan tool to confirm the system has gone into closed loop control, if it remains in open loop control there will be no STFT or LTFT corrections and the system will be using substituted values. Check to see if the O2 sensor starts switching when held at 2000 rpm, if no then I would recommend "force" rich and lean testing of the sensor to see if it responds.

[ww1dm1]

Alright, took a closer look at the oxygen sensor response. Here are the results of the front oxygen sensor. Values are in closed loop mode (engine at operating temperature):

IDLE
Voltage output: constant 0V
Short Term Fuel Trim: constant 0%

~2000 RPM
Voltage output: constant 0V
Short Term Fuel Trim: constant 0%

~3000 RPM+:
Voltage output: 0-1V oscillation
Short Term Fuel Trim: variable negative (-6ish %)

What puzzles me is that at idle and up to ~2500RPM both the voltage and short fuel trim are zero. I thought 0V output should increase the fuel trim as a response?

Also, the rear oxygen sensor is at constant 1V regardless of RPM, so I assume it's dead. As far as I know it's main purpose is monitoring the condition of the catalytic converter, does it affect the fuel trim on Volvos?

[Clan]

Originally Posted by ww1dm1

My front oxygen sensor voltage is constantly zero at idle, which as I understand means a positive STFT. I believe that should keep increasing the LTFT until voltage oscillation occurs. If I recall correctly, when I push the throttle the voltage shoots up to 1V and immediately goes back to zero again. I'll have to check again, this is some good information. I'm using ELM327, live data is available for the oxygen sensors.

if there is no output from the oxygen sensor at idle suspect the internal heater , as it seems to work at higher rpm when the exhaust heats it up . An oxygen sensor will not work unless it is over 300 C or some temp around that figure ... The heater is there to heat it up when cold or idling .. Check the Oxygen sensor heater fuse ..

The rear oxygen sensor should stabilize at around 0.7 v if all is well when properly warmed up .

[KBB]

At idle and at 2000 RPM the sensor is not switching the ECU will not believe that it is in closed loop and during that stage STFT is disabled hence why you are not seeing any reaction. At 3000 RPM combustion gases are hot enough to bring the sensor on line and it starts switching so STFT can now take place.

Agree with Clan that the could be an issue with the heating circuit but they do normally and reliably flag a DTC for a failed heater circuit be it no supply voltage through an open circuit or fuse or the heater coil has gone open circuit. It could be that the heating coil is just worn out and the ECU is seeing current flow but the coil is producing no heat.

I have dealt with many wiring faults over the years on O2 sensors so it worth a visual inspection just to make sure the sensor harness is not coming in contact with the hot exhaust under engine torque momentarily shorting the signal wire to ground.

Some simple tests are to disconnect the sensor key on engine off scan tool connected. The ECU self diagnostics run a bias line voltage on the signal wire, when disconnected the scan tool should see around 0.45 volts this would prove the signal wire is good (signal wire purple ECU side). Next jump the purple to the black/white wire (sensor ground via ECU), if scan tool O2 voltage drops to zero then ground is good.

Heater supply wire (red/black) test for system voltage use a test light with about 1 amp draw connected to red/black and ground. Next test heater ECU control connect test light to battery positive run engine and then touch the Green/white wire. The light should pulse fast as this is ECU ground side switched pulse width modulated circuit.

If the wiring tests out good then I will describe the forced rich lean test to confirm sensor is failing.

[ww1dm1]

A heater problem would make sense, the fuse is good though. I read the codes with another cable and VolFCR, here's what I've got:

EFI-212 Front heated oxygen sensor (H2OS), signal faulty
EFI-435 Front heated oxygen sensor short-term fuel trim signal faulty
EFI-512 Short term fuel trim, changes too quickly
EFI-522 Rear heated oxygen sensor (H2OS) preheating circuit fault

Strangely there's no bad heating circuit error for the front sensor and no missing signal error for the rear sensor, like it's switched up. I assumed that the software considers the front sensor to be "Bank 1 Sensor 1" and the rear one to be "Bank 1 Sensor 2", but I am not too sure about that anymore, maybe it's backwards.

I'll try the manual tests as you instruct.

[ww1dm1]

Alright, I'm really pulling my hair out here. Went to do the tests, reading oxygen sensor value while the front sensor is disconnected without the engine running gives me the same 1V as before. The color coding was different as well, so decided to put off further tests until I figure it out. Also couldn't find the connector for the rear one, expected to find it next to the front one, but all the other connectors nearby are 2-3 pin.

Important part now - took another look at the oxygen sensor values again. I warmed it up, cleared the DTCs and switched to LPG. To my surprise the front sensor was showing a proper oscillation and a small fuel trim even at idle, it seemed to be working as it should and didn't throw any DTCs for the front sensor.

However as soon as I switched back to petrol again the short term fuel trim started climbing until it reached ~40% and suddenly dropped down to zero. I assume that's when it set off a DTC and stopped taking the fuel trim into account. And after that I found the same EFI-212 and EFI-435 for the front sensor. If I'm not being clear enough I saved some graphs I could upload.

So basically, I believe the front sensor is fine (rear one still seems to be dead), I just have a morbidly high fuel trim on petrol. And it can't be vacuum leaks. I think I do have a small one or two, but it runs more or less fine on LPG and very unreliably on petrol.

EDIT: Unless... as far as I know LPG runs hotter than petrol. If LPG exhaust gas alone is hot enough to maintain proper oxygen sensor temperature and after switching to petrol it drops down then maybe the voltage starts rising as it cools untill it reaches 1V and shows us rapidly rising fuel trim. Does it run that much hotter?

[960kg]

In Vadis EFI-522 Rear heated oxygen sensor (H2OS) preheating circuit fault
is also the same error code for the Front O2 sensor heater.

You have to look at the list of codes carefully as it is easy to miss.

DTC`s don`t necessarily happen instantly! Just like it may take so many cold starts to disable them completely although erased by yourself.

The connector on the rear O2 sensor was up on the bulkhead in 1997 version (with the longer connecting wire) but moved in 1998 to behind the centre console with the (shorter wire and a sealing bung) on the left side when sitting in the car. If you remove the side panel the connector is up on the metal struts.

The rear sensor on the T4 does effect fuel trim as it not only reports back about the cat. The front and rear sensor communicate with one another.

Why don`t you disconnect the battery overnight so that everything can reset in it`s own time and start taking readings again?

OK, so i have been condemned before as the proper way is not my way and as you can see your pulling your hair out and frustrated as you can`t read what you want it to read .....you can see that you have problems with the sensors or wires so i just replace and job done with and move on......also it is cheaper fuel wise with a reliable motor again.

[ww1dm1]

Originally Posted by 960kg

In Vadis EFI-522 Rear heated oxygen sensor (H2OS) preheating circuit fault
is also the same error code for the Front O2 sensor heater.

You have to look at the list of codes carefully as it is easy to miss.

DTC`s don`t necessarily happen instantly! Just like it may take so many cold starts to disable them completely although erased by yourself.

The connector on the rear O2 sensor was up on the bulkhead in 1997 version (with the longer connecting wire) but moved in 1998 to behind the centre console with the (shorter wire and a sealing bung) on the left side when sitting in the car. If you remove the side panel the connector is up on the metal struts.

The rear sensor on the T4 does effect fuel trim as it not only reports back about the cat. The front and rear sensor communicate with one another.

Why don`t you disconnect the battery overnight so that everything can reset in it`s own time and start taking readings again?

OK, so i have been condemned before as the proper way is not my way and as you can see your pulling your hair out and frustrated as you can`t read what you want it to read .....you can see that you have problems with the sensors or wires so i just replace and job done with and move on......also it is cheaper fuel wise with a reliable motor again.

You mean the code for rear and front sensor heater fault is the same? Thats's odd. I did find the rear sensor connector, seems like the heater really is dead. Could the rear sensor alone cause such strange behavior as rapidly rising front sensor fuel trim?

[ww1dm1]

Originally Posted by KBB

Some simple tests are to disconnect the sensor key on engine off scan tool connected. The ECU self diagnostics run a bias line voltage on the signal wire, when disconnected the scan tool should see around 0.45 volts this would prove the signal wire is good (signal wire purple ECU side). Next jump the purple to the black/white wire (sensor ground via ECU), if scan tool O2 voltage drops to zero then ground is good.

Heater supply wire (red/black) test for system voltage use a test light with about 1 amp draw connected to red/black and ground. Next test heater ECU control connect test light to battery positive run engine and then touch the Green/white wire. The light should pulse fast as this is ECU ground side switched pulse width modulated circuit.

If the wiring tests out good then I will describe the forced rich lean test to confirm sensor is failing.

Alright, according to the color coding of the wires (red-white-black-yellow) I probably have titania sensors, which are a little different from zirconia. These instead of generating voltage on oxygen concentration difference just change their internal resistance. Might be why disconnecting it does not show me constant 0.45V. Anyways, found the pinout (attached) and did a heater element test. Don't really have a lamp that draws 1A at 12V, so I simply connected an ammeter in the circuit. Front sensor showed ~1.2A that was kind of jumpy, so I'm guessing it's pulsed as you said. I also checked the resistance of the heater element, it was ~7 ohm, which I assume is good. For the rear sensor - no current and 10kohm resistance, I guess it's toast, no surprise.

So basically, the front sensor still seems fine. The heater element seems to work and the signal is good on LPG.