Correct /expected Intake air Temperature

[cheshired5]

You've reached your minimum posts for pm privileges so maybe contact forum admin.
The next batch isn't with me yet but should be by the weekend so I'll be contacting everyone then.
I only take money after they're tested and ready to go.

[osullivant]

Originally Posted by cheshired5

Checked Vida and it turns out you have 2 intake air temperature sensors..... Lucky you.
One in the MAF and one in the MAP so do a similar test on the MAF.
Don't spend big on a MAF if the temp element is defective, in fact I might have one cheap if you need one but you'll need to check the sensor number.
Watch this video to see how to do this.

That makes some sense except there is only one output on Torque showing intake temperature and when I disconnected the Tmap sensor this input failed to minus 41 and warned of frost, when reconnected and cooled with a shot of maf cleaner the outputted temperature dropped and as the sensor warmed up it rose so no doubt the Map sensor is contributing to the engine perceiving an intake temp of approx 25 over ambient, possibly this is a composit of two inputs. my maf has only 4 wires, no screws on the sensor and bosch part numbers on the casing/tube...

[cheshired5]

Hmmm cunning design on your MAF.
It'll still be two pieces though, it's more whether they can be separated in a non destructive way.

Vida does allow both temperatures to be read or at least it looks like it does. It has two separate entries but I haven't got a suitable vehicle to confirm so wait to see what that says.

[osullivant]

This is becoming more complex....

got access to VIDA last nght courtesy of a helpful forumite......

The temperatures of the tmap and maf were both read on Vida last night. both were showing 25c over ambient.

fault 2900 was shown as exhaust temperature/ catatylic convert temperature sensor, took this out and tested it and it seems fine, (its impedence changes with changes in temperature)

The fault shows as the same whether or not the sensor is unplugged.

so I have three temperature related sensors, all showing faults and all appear to be functioning, the Tmap is new and behaves exactly like the old one.

I have checked all wiring back to the ECM there are no shorts or breaks.

The maf had nothing connected to the Brown/black wire and appeared to be no earth to the MAF so I took this wire to Ground with a jumper from mid point.... the car drives much better but still very lumpy, but interestingly the intake air temperature (as viewed on torque) is now only showing as being about 9c above ambient.

I do not know where the earth/negative for the ECM is connected, my last hope is that this is a problem otherwise I think it must be an interbal ECM problem.....

open to thoughts.... where does one get the ECM checked/ repaired? has anyone looked inside one? It seems to be sealed with some sort of glue... I would not be surprised to see some water damage in it

[SwissXC90]

I experienced not so dissimilar problems to yours on an old VW Golf many many years ago
The ECM thought the car was too cold, and was setting the petrol mixture to maximum rich, resulting in poor start and impossible to drive.
All due to a broken ground wire on the engine temperature sensor, which made the ECM think the engine was at -50 degrees.

So I would definitely be checking the gronds on the ECM and related temperature sensores

Reading your posts you say you were working on the engine. So focus all your attention primarily to everything that was disturbed in the areas you were working on. Eg: if you were working on the right hand side of the engine, then the chances of a wire break or terminal corrosion issue on the left hand side are small. Focus on the work area.
Sometimes connectors can get dirty and corroded but operate without any sign of trouble until they are moved/bumped/wiggled/unplugged and replugged. Then the contact issues may appear. So ask yourself where you were working and what you were doing, and what you disconnected and reconnected.
Clean any connector contacts with contact cleaner, ensure they are free of dirt, grime and oil.
Ensure the connectors mate properly and that you feel some physical resistance when connecting, this indicates the pins have the proper friction fit with each other.
Loose pins can be as bad as dirty pins.


I couldn't see what vehicle you have but know you have a D5 diesel engine so my notes below are based on a 2009 XC90 with the 185hp D5 diesel engine. Most vehicles are wired in a similar manner so the notes will have some degree of relevance.
To get specific details for your car, let me know what car you have (model and the MY please).

The MY2009 XC90 has the following ground points for the ECM.
Inspect the ground points, ensure the bolts are tight. If you disconnected the grounds when working on the engine, make sure you didn't forget to reconnect a ground. If you disconnected any ground, then undo the bolt again, inspect for clean, oil-free terminals and do the bolts up tight (but please do not snap them, as tight as a 1/4 inch drive controlled by a human can get them is enough)

Primary engine bay grounding points:

31/2 Left MacPherson strut tower
Grounds for:

• 4/71 Cooling fan control module
• 4/46 Engine Control Module (ECM), 6-Cyl., 8-Cyl., Diesel

The ECM grounds are on ECM pins B2, B4, B6. These pins go each with a BLACK wire to junction 53/395, then onwards with a single BLACK wire to grounding point 31/2 Left MacPherson strut tower

31/96 Right MacPherson strut tower
Grounds for:

• 4/46 Engine Control Module (ECM) (SB wire)
• 4/71 Cooling fan control module, 8-Cyl. / Diesel / 6-Cyl. (SB wire)
• 9/32 PTC resistor, crankcase ventilation (SB wire)

The ECM grounds on ECM pins A53, A54, A63. These pins go each with a SB wire to junction 53/326.
NOTE: 9/32 (PTC resistor, crankcase ventilation) also is connected with a SB wire to junction 53/326
Junction 53/326 connects with a single SB wire to grounding point 31/96

31/4 Engine

• 31/44 Ground connection - a big fat grounding cable

31/44 Left-hand side member, lower engine compartment

• 31/4 Ground connection - a big fat grounding cable

NOTE: SB wire is a BLACK wire
So carefully check all the grounding wires points at the strut towers.
Inspect for any sign of corrosion.
Measure impedance from ECM to the strut towers, and then from the ECU to any other good grounding point.
Check voltage drop when ECU is turned on (engine does not need to be running). Expect less than 0.1V voltage drop. Should be so small to be insignificant.
Check also the engine block ground (31/4, 31/44) is secure, although this is not so relevant to a lot of the engine controls, it is there mainly as a safety ground, starter motor negative ground, and to prevent issues when the engine doesn't grounded via other metal parts.

Also check the following:

7/17 Mass air flow sensor (MAF), Diesel is wired as follows:
Pin 1 GN is the 12V supply via fuse 11B/14
Pins 2 BN-SB, 3 GR-R, 4 GR-W are the 3 feeds direct to the ECM.
MAF pin 4 GR-W connects to ECM pin A86
MAF pin 3 GR-R connects to ECM pin A59
MAF pin 2 BN-SB connects to ECM pin A29

Logically, based on wire colours, it makes sense that BN-SB is a ground wire and I would expect to find ground on it, BUT it grounds inside the ECM (and not externally).
Why? Because a MAF is a sensitive device and to prevent noise on the signals it must be grounded at the control unit that is reading the signals.

7/105 Outside temperature sensor, engine control module T5 PETROL ONLY, sorry
NOTE that the ECM has an outside air temperature sensor which on the XC90 is mounted on the left hand side wing mirror on the door for the T5 Petrol Engines (not applicable to D5 Diesel engines)
7/105 Outside temperature sensor, engine control module
this connects with
OR-W wire (signal side) to pin B29 of the ECM
BN wire (expect this to be ground side) to pin B4 of the ECM
It will be a thermistor so you can measure resistance and the resistsance will change with temperature
NOTE that the wires running through the door into the body have a tendency to break due to continued flexing, so if you have any suspicion of wire continuity issues (measure the from wing mirror to ECM) then the first place to look is inside the wiring loom from left front door to body.


7/165 Pressure and temperature sensor, intake manifold
This is another temperature sensor worth checking.
This is cabled with 4 wires direct to the ECM
Pin 1 Y-SB goes to ECM pin A87
Pin 2 Y-W goes to ECM pin A85
Pin 3 Y goes to ECM pin A82
Pin 1 Y-W goes to ECM pin A15
Check for continuity and corrosion.

7/16 Sensor, coolant temperature
This connects with 2 wires direct to the ECM
Pin 1 GR-R to ECM pin A60
Pin 2 BN-SB to ECM pin A56
The BN-SB will surely be the ground side
A coolant temp sensor is mostly a thermistor so the resistance with vary with temperature, easy to test.


Wire colours used in Volvo wiring diagrams:
BL = Blue
BN = Brown
GN = Green
GR = Gray
NL = Natural
LBL = Light Blue
LGN = Light Green
OR = Orange
P = Pink
R = Red
SB = Black
VO = Violet
W = White
Y = Yellow

[osullivant]

Thanks for that useful post, it must have taken some considerable time to create.

Your are correct in that it is a 2006 D5185. I have done in a piecemeal fashion, most of what you advise, but I will go back through it again, using your scheme as a blueprint and hope for the best.

I will pay particular attentention to the grounds...

Regards


Tony.

[SwissXC90]

Originally Posted by osullivant

Thanks for that useful post, it must have taken some considerable time to create.

You are welcom, it was just some cut and past from the wiring diagram, combiner with common sense and experience.

[osullivant]

Even more puzzeled than ever.

No earths on A53 A54 A63 and no Black wires in the connection...... I have looked at the wiring diagram and I see that those should be earths heading towards the PTC resistor but is there one of these in a D5 I thought the PCV nipple is heated with water so no electrical element.... so it seems no earths going into A connection on the ECM but plenty coming out presumably these come from the B side.

solid earths on B2 B4 B6

I have remembered that the day before its last "without Fault" journey was home from having a tow bar fitted, ( That night the wood pecker came to live in the engine in the form of unwell tappets.)

is it possible that the towbar connecting which seems to consist of splice connections onto the rear lights with a box of tricks that presumably is some sort of relay being connected to the rear cigarrette lighter socket.I have disconnected all wires that I can find and taped them up carefully so probably not now an issue but could a few circuits have been fried if the fitter was working on a trial and error fashion.

Unless someone can come up with a good reason not to I am going to open the ECM tomorrow and have a look, I think a hot air gun will assist in removing the sealant/glue that keeps the cover on...

Tony.

[osullivant]

Opened up the ECM. Corrosion on the board under the vent...... cleaned it off and things have changed dramatically.... see my new thread.... SIck ETM...

[SwissXC90]

Originally Posted by osullivant

Opened up the ECM. Corrosion on the board under the vent...... cleaned it off and things have changed dramatically.... see my new thread.... SIck ETM...

Great news that you have found a positive cause of the problem

The path forward should now be clear...