Pre+Post Cat / Lambda / Oxygen sensor tests - help needed with results...

[mrjonsavage]

Been testing my Pre & Post Cat sensors via VCDS & good old fashioned multimeter & need bit help deciding what results mean...
Used the Volkswagen Workshop Manuals online;
pre cat : Motronic injection and ignition system (2.0 ltr. engine)
post cat : Motronic injection and ignition system (2.0 ltr. engine)

For the pre-cat I get the following results;
Via VCDS:
display zone 1: 80 Ohms (spec: 6.4-47.5 Ohm) [very high obviously]
display zone 2: Htg.S1.ON (NOT alternating to 'OFF')
Via multimeter:
Continuity between pins 1+2: GOOD
Voltage between pins 1+2 as engine idles: NO VOLTAGE & NO alternating between Htg.S1.ON/OFF (as above)
Don't have a test box 'VAG 1598/22' (2k price to buy online?!)

For the post-cat I get the following results;

Via VCDS:
Display Zone 3: 15 Ohms (spec: 6.4-47.5 Ohms): GOOD
Display Zone 4: Htg.S2.ON (NOT alternating to 'OFF')
Via multimeter:
Continuity between pins 1+2: GOOD
Voltage between pins 1+2 as engine idles: NO VOLTAGE & NO alternating between Htg.S2.ON/OFF (as above)

SO, this would seems to indicate that the Pre-Cat has too high a resistance, continuity, but no voltage when engine idling. For the post cat, within tolarance resistance, continuity but no voltage when engine idling.

Now, went on to do the VCDS Engine Measured Blocks tests:
Block 002: No MAF sensor (1.6 SE DOHC engine, MAP sensor but can't find where this is located to test on VCDS [any ideas?])
Block 030: Oxygen Sensor Regulator: Field1: 1 1 1/0 when rev's, Field2: 1 1 0 (NO fluctuation) : OK?
Block 032: Oxygen Sensor Learned Values: F1: -10.0% (other test=-3.0%), F2: 0.0% : Running rich at the pre-sensor?
Block 033: Pre-Cat Oxygen Sensor Control: F1 -2.0-0.0% fluctuation: OK?
Now via Basic Settings in VCDS Engine:
Block 036: Post-Cat Oxygen Sensor Control: F1: 0.756V (0-1V = ok), F2: B1-S2 OK: = Post Cat good?
Block 034: Ageing of Pre Cat Oxygen Sensor: F3 (0.81/0.88 [2nd test] (Must be > 0.8 [new sensor = 1.99]): So Pre Cat JUST on line of being ok?
Block046: Lambda: F3: 94.5% [2nd test: 87%], F4: CAT B1 OK : Catalytic Convertor OK?

SO: What's your ideas from this & please no glib 'it's f*cked mate', put down why you think what you do even if it's obvious to you. Anything else to test here for the Pre/Post/Cat itself?!

[Crasher]

Which version of VCDS do you have? Full VCDS has a readiness code function that tests the sensors and tells you if they are OK or not, determining their health even from the comprehensive info you have proved if very difficult. Which year and engine code as the data suggests 1.6 16v and 2.0 8v which contradict each other?

[mrjonsavage]

Which version of VCDS do you have? Full VCDS has a readiness code function that tests the sensors and tells you if they are OK or not, determining their health even from the comprehensive info you have proved if very difficult. Which year and engine code as the data suggests 1.6 16v and 2.0 8v which contradict each other?

VCDS 10.6

1.6. SE '03 BCB 105bhp 77kW

Will look at the 'readiness' option & try.

Links above mysteriously changed (may have been moderated?!)

[Crasher]

Carrying out the readiness tests in Basic Settings between groups 028 to 75 varies (and more on some models with such devices as Secondary Air Injection and variable cam timing) from car to car but if you persevere with it this test can tell you how the emissions system is working. I have tried to tailor these to the BCB engine with some additions of my own that I have found but there may be a few errors as I have written this mostly from memory.

INSTRUCTIONS FOR SETTING THE READINESS CODE WITH VCDS

PREREQUISITES

Vehicle stopped
Vehicle not parked over a flammable surface such as wood or grass
Vehicle in a well-ventilated non enclosed space
Vehicle in neutral
Handbrake applied
All electrical components such as lights and rear window heater must be switched off
The battery must be fully charged.
The coolant temperature must be at least 80°C
The intake air temperature must be below 60 °C
The throttle body must be spotlessly clean inside
Fuel tank more than 1/4 full

PROCEDURE

Connect the VCDS cable to diagnostic socket
Turn on the ignition and select “01-Engine”

CLEAR THE FAULT MEMORY

Select “Fault Codes - 02”
Rectify any faults found and then select “Clear Codes - 05” to erase the fault memory
If no codes are found, erase the fault memory anyway as the readiness code is reset each time the fault memory is erased
Select “Done, Go Back”

MATCH THE THROTTLE BODY TO THE ECU

Select function 04 “Basic settings - 04”
Click on “Group” and enter the value 060, Click “GO” or press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of the display
Readout on display in field 4 “ADP. Run”
This should change to “ADP. o.k.”
Display field 3 should read between 0 and 8
The abbreviation “ADP” in display field 4 stands for “Adaption”, which in fact means adaptation
Wait for 30 seconds after “ADP OK” appears, then exit “01-Engine” and turn off the ignition, wait for 30 seconds and turn the ignition on again and wait another 30 seconds.
Start the engine
Go back into “01-Engine” and Select function 04 “Basic settings - 04”

CHECKING THE KNOCK CONTROL SYSTEM

Select “Group” and enter the value 028, press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of display
Depress brake pedal and accelerator simultaneously
Run engine at ECU set increased speed; the display in display field 4 will then switch from “Test OFF” to “Test ON”
Run engine until display field 4 indicates specified value “System OK.”

CHECKING THE LAMBDA PROBE AGEING

Select “Group” and enter the value 030, Click “GO” or press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of the display
Check the operating state of lambda control display fields 1 and 2
Specified value display field 1: 111
Specified value display field 2: 110
Note, this may take a few minutes at idle or even require the rpm to be raised to around 2500>2800rpm for a minute or so
The first position in the 3-digit numerical block fluctuates initially between 0 and 1 (lambda probe heater off and on)
The lambda control of lambda probe downstream of catalyst is not active without engine load and the third position in display field 2 indicates 0

AGEING TEST OF THE LAMBDA PROBE BEFORE CATALYST

Select “Group” and enter the value 034, Click “GO” or press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of the display
Depress the brake pedal and accelerator simultaneously, some engines only require the brake pedal to be depressed
Engine speed is increased and set by the ECU and the readout in display field 4 switches from “Test OFF” to “Test ON”
Catalytic converter temperature in display field 2 must be at least 350 °C. This may take a few minutes
Run the engine until display field 4 indicates specified value “B1-S1 O.K.”

CHECKING LAMBDA PROBE PREPARATION DOWNSTREAM OF CATALYTIC CONVERTER

Select “Group” and enter the value 036, Click “GO” or press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of the display
Depress the brake pedal and accelerator simultaneously, some engines only require the brake pedal to be depressed
Engine speed is increased and set by the ECU, the display in display field 4 will then switch from “Test OFF” to “Test ON”
Run the engine until display field 4 indicates specified value “B1-S2 O.K.”

DIAGNOSIS OF LAMBDA CONTROL SYSTEM

Select “Group” and enter the value 037, Click “GO” or press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of the display
Depress brake pedal and accelerator simultaneously, some engines only require the brake pedal to be depressed
Engine speed is increased and set by the ECU, the display in display field 4 will then switch from “Test OFF” to “Test ON”
Run the engine until field 4 indicates specified value “System OK.”

AGEING TEST OF LAMBDA PROBE AFTER CATALYST

Select “Group” and enter the value 043, Click “GO” or press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of the display
Depress brake pedal and accelerator simultaneously, some engines only require the brake pedal to be depressed
Engine speed is increased and set by the ECU and the readout in display field 4 switches from “Test OFF” to “Test ON”
Continue running engine at higher speed until the catalytic converter temperature in display field 2 shows at least 200 °C. This may take a few minutes
Run the engine until display field 4 changes from “TEST OFF” to “TEST ON” and then to the “B1-S2 O.K.”

CATALYST DIAGNOSIS

Select “Group” and enter the value 046, Click “GO” or press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of the display
Depress brake pedal and accelerator simultaneously, some engines only require the brake pedal to be depressed
Engine speed is increased and set by the ECU and the readout in display field 4 switches from “Test OFF” to “Test ON” but on some engines the throttle has to be held to set speed to 2500...4500 rpm
Catalytic converter temperature in display field 2 must be at least 400 °C and this may take a few minutes
When the readout in display field 4 should changes from “Test OFF” to “Test ON”, maintain the speed until the readout in display field 4 shows the specified value “CatB1 O.K.”

TESTING THE TANK VENT SYSTEM

Depress the brake pedal
Select “Group” and enter the value 070, Click “GO” or press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of the display
The readout in display field 4 should switch from “Test OFF” to “Test ON”
Run engine at idling speed until display field 4 indicates specified value “TVV O.K.”

ADAPTING THE EGR VALVE TO THE ECU

Exit “Basic settings - 04”
Turn off the engine, turn the ignition back on
Wait for VCDS to reset itself back into “01-Engine”
Enter “Basic settings - 04”
Select “Group” and enter the value 074, Click “GO” or press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of the display
Readout on display in field 4 should say “ADP. Run” but this may happen so quickly you do not see it
The value should change to “ADP. o.k.”

TESTING THE EXHAUST GAS RECIRCULATION SYSTEM

Select “Group” and enter the value 075, Click “GO” or press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of the display
Rev the engine quickly to high revs and allow the revs to fall, in field 4 “Test Off” should change to “Test on” and then to “System OK”. If this does not happen after a few attempts, take the car for a run where the engine speed must reach at least 1800...3600 rpm. Get the car up to a speed of approx 30 mph and in 3rd gear, allow the engine to run on trailing throttle for at least 8 seconds down a hill until “TEST ON” appears and “SYSTEM OK” is displayed. During this process the lap top MUST be operated by an assistant sitting in the back of the car
Select function “Meas. Blocks -08”
Select “Group” and enter the value 075, Click “GO” or press the Enter key or on some cars, click on “ON/OFF/Next” box in upper right of the display
Perform brief drive (approx. 3...4 min)
Engine speed must reach at least 1800...3600 rpm, coolant temperature greater than 70 °C
Rapidly take your foot off the accelerator pedal, this will generate the trailing throttle phase
The readout in the display field 4 switches from “Test OFF” to “Test ON”
Trailing throttle phase must last approx. 8 seconds
Check display field 4: Specified value: Syst. o.k.
If this message is not displayed, trailing throttle phase must be repeated a number of times

[awmackay]

Resurrecting a thread from the past, but Crasher would the tests you've posted be applicable to a VW polo 1.4 bby engine also?

[Crasher]

Yes they pretty much apply to any petrol engine with the readiness facility, there are small model variations such as cars without EGR or secondary air injection and I tend to use VCDS as it is quicker than VAS PC which has a targeted function for each car but the VCDS readiness function, where shown, is rubbish. I go into Basic Settings and start at about 028 and then work my way up (I hate it when you have to type in each number rather than just use the up arrow as you do on some cars) and work my way through to around zone 75 (as high as 128 on some cars) which is EGR valve testing and then look back at the readiness box to see if all is OK. There are even a couple of tests that come up that are not in the list such as 028 fuel injection test. You can tell what is going on in each block as anything relevant will come up as "TEST OFF" in block 4. To do the test you need to have your foot on the brake pedal and some tests such as the cat efficiency can be a real pain to get to engage, requiring you to keep playing with the revs around 2000 rpm until you hit that sweet spot and some cat tests won't initiate until the cat temp is over 440 degrees. It's a very useful, not perfect, way of validating your work so that when you give the customer the car back you can be reasonably sure the light is not going to come back on, as they do not tend to understand that it can come on for dozens of different reasons, to them it is the same fault again. It does not always show up a weak cat (typically the 3 cylinder models) but it does prevent a lot of come back which is one of my biggest hates as it undermines customer confidence which is hugely important to me. One very important point is to never go into group 060 with the engine running as this will store a fault code and mean you have to clear it and start again. Before doing the readiness you should clear the learnt values in Adaptation 00 and the align the throttle body in 060 then do the readiness.

[awmackay]

Yes they pretty much apply to any petrol engine with the readiness facility...

Thanks Crasher, will give it a whirl this afternoon

[awmackay]

Hi Crasher,

Thanks for the guide and advice. I did all the tests as described and every one passed with expected results - readiness is now all "passed".

The only query I have, is that when I did the throttle body adaptation (060) the value in field 3 (self adaptation steps counter) was 12. In your previous post you said this should be 0-8, is this just different because it is a different engine?

Thank you

[Crasher]

Yes I see that value vary a lot, often 9 when specified at 7, on certain engines 11>12. On the BBY the basic setting procedure will only end once the counter in display field 3 has reached 12.

[awmackay]

...the BBY the basic setting procedure will only end once the counter in display field 3 has reached 12.

Perfect, thanks Crasher