Hello,

My trusty 2009 Superb, which I've had for nearly 7 years, has gone into limp mode for the first time. An engine scan shows up the P0238 error.

The MAP sensor (marked as #1 on the image) on the CBBB is very awkward to access. I've managed to access the sensor from the inside the tube by removing the upper rubber hose section. I gave the sensor a decent clean with a toothbrush, sprayed it with alcohol and electronics cleaner, and blasted it with compressed air a few times. I also had the rubber section at the bottom removed, so all the excess alcohol/spray would leave through the bottom part of the rigid plastic section.
The car was fine for some 3 miles with lots of power, but then the error came back on a 60mph road.

 

From my understanding, the sensor might be faulty, or the wiring loom might be faulty (no continuity), or there might be something else that's causing the issue (DPF, EGR?)

 

So my question is, the Skoda manual recommends to remove the fan shroud in order to remove the whole rigid plastic assembly with the sensor, is this the only way to change the sensor?

7 minutes ago, mizuno said:

gave the sensor a decent clean with a toothbrush, sprayed it with alcohol and electronics cleaner, and blasted it with compressed air a few times

You probably only cleaned the intake air temperature sensor, which is usually the only visible/accessible part of this combined sensor.

Compressed air would probably damage the actual pressure sensor if you managed to direct any into it.

 

Can't help you with access to change sensor, but do you have enough to get the connector off? (thinking in terms of checking wiring).

If you still have it, might be idea to post your diagnostic log.

 

My understanding of this circuit is that it feeds 5V into the sensor, and it should return a variable value back to the ECU.

 

0.5V gradually increasing, and I think at 4 or 4.5V it will put car into limp mode for protection.

 

 

As mentioned, you might be worth trying to get plug off if possible to see if car is feeding correct Voltages, no shorts etc.  Then try to give the loom a wiggle test.

9 hours ago, Breezy_Pete said:

You probably only cleaned the intake air temperature sensor, which is usually the only visible/accessible part of this combined sensor.

Compressed air would probably damage the actual pressure sensor if you managed to direct any into it.

 

Can't help you with access to change sensor, but do you have enough to get the connector off? (thinking in terms of checking wiring).

Thanks for the reply. I only could use the compressed air nozzle from a good distance, so I hope I did not cause any damage. Good to know in case I ever need to clean the sensor again once this is sorted.
I did read some info regarding that the MAP sensor is a two in one sensor on some engines and just a pressure sensor on other engines, thanks for clarifying that.
Even taking the connector off is tricky, I suppose I could try to press on the plastic clip with a screwdriver to release the connector, and then gently tug on the loom to get the connector off. I'll give it a go tomorrow.
 

 

9 hours ago, varooom said:

If you still have it, might be idea to post your diagnostic log.

 

My understanding of this circuit is that it feeds 5V into the sensor, and it should return a variable value back to the ECU.

 

0.5V gradually increasing, and I think at 4 or 4.5V it will put car into limp mode for protection.

 

 

As mentioned, you might be worth trying to get plug off if possible to see if car is feeding correct Voltages, no shorts etc.  Then try to give the loom a wiggle test.

Thanks for the reply. I can't get the exact voltage from the odb2 reader and the Car Scanner app, but I am able to view the calculated (expected) pressure and the real pressure. This morning the car was giving good readings when I was revving the engine on park, and then all of a sudden it started consistently giving around +0.3 bar even on idle. So something's going on there.

The log has got loads of errors (seemingly non engine related) and is a bit confusing to read, but I'll clear all the errors tomorrow, re-scan it and post the log.
You gave me an idea, I could try wiggle the loom with the engine running and see if the reading changes at all.


By the way, I've ordered an exact replacement part. I had to put an endoscope camera in there to see which model the sensor is, and the label was completely covered with oily dirt. I've crumpled up a paper towel, soaked it with an electronics cleaner and put it in a pick-up tool/claw thing and managed to clean the label just enough to read the part number.

It might be an idea to post both logs, what can sometimes seem irrelevant might actually be related.

 

I have had a CBBB engine before, goes well when remapped 🤩

On 27/07/2022 at 22:26, varooom said:

It might be an idea to post both logs, what can sometimes seem irrelevant might actually be related.

 

I have had a CBBB engine before, goes well when remapped 🤩

I might get mine remapped at some point, but at the same time there's plenty of power available with the 170 

Back to the main subject of the topic - I've fixed it!

Long story short: there was a broken wire immediately after the intermediary loom.

Long story long:

Quote

Thinking that the sensor was the problem, I've ordered a new sensor from a well known diesel company. Did as much as I could, but screw #6 was so problematic to access, I actually managed to strip some of it. Defeated for the day, I resumed in the morning.
 

Saturday morning I've managed to position myself better under the engine to try and access screw #6, and with all my might I managed to loosen it. After that that I managed to pull out the rigid boost pipe. With the pipe pulled out, I could then disconnect and remove the old sensor.
 

I've put a new sensor in, connected everything up, put everything back together except for the engine undertray. Turned on the ignition, cleared the errors, turned the engine on, everything seemed fine for a minute and then the dreaded P0238 came back. ****.
 

So I thought, ok, there must be a continuity break somewhere. Took everything out again, this time I was quite a bit quicker as I knew what to do in what order. Then I've watched a few videos diagnosing the same problem, got my old trusty multimeter out and started poking around. Tried testing the continuity of the intermediary loom and it all seemed fine.
 

So then I though, right, I will need to access the ECU connector to see if there's continuity to the ECU. In order to access the ECU I needed to take the plastic off just below the front windshield, and in order to take the plastic off I needed to take the wipers off. Taking the wipers off was a major pain, but a tip from a youtube video helped me loads.
 

With the wipers taken off, I took the plastic trim off and I could see the ECU. Little did I know that to remove the ECU connector I would need to grind a slot into the security bolts so that I could use a flat head screwdriver. As fate would have it, I ordered a dremel the day before but it would only be delivered on Sunday.
 

Defeated, I've put the ECU, the plastic trim and the wipers back. At this point I was doubting myself, should I give up and take the car to a garage? Had a little break, had another tea, and then I pressed on. I kept looking at the wiring loom, kept going under the engine, and towards the second half of the day I had my big discovery. While under the car, I saw this tiny little broken wire. I couldn't blame myself for not seeing it earlier, really it was quite difficult to see. The intermediary loom was fine, but the connector that connects to the intermediary loom had a broken wire. This was most probably of the plastic protector that wrapped around the four wires to protect them. Except that it had quite a sharp edge which eventually broke the wire off.

I've tested the continuity into the broken wire that was leaving the connector, and I've confirmed that this was the wire that was responsible for the pressure reading from the sensor. That wire is purple when it goes into the intermediary connector and then is switched to green with gray stripes when it leaves the intermediary connector.

I got myself a nice length of cable speaker and pulled the red wire off. Got myself a pair of heat shrink solder sleeves, and set to work. Working on the connector that goes into the MAP sensor was quite straightforward, but working under the engine to attach the second part of the replacement wire was a bit of a faff. A gas torch on a low flame provided plenty of heat to shrink the sleeve and melt the solder, connecting everything together. Then I used loads of self amalgamating tape to add further waterproofing and friction protection, and a few zip ties to tie the new replacement wire to the old wiring loom.

Put everything back together except for the engine undertray, turned the ignition on, cleared all the codes. Started the engine and voila! All was fine. I've fixed the engine undertray back, and by 10PM on a Saturday I had my old car back. Went for a test drive on a nice wide 60mph road and the Superb drove like a dream, with loads of power.

Access to the sensor would be much easier if it weren't for the AC unit. This is probably the only time I wished my car didn't have AC. All the rigid rubber AC pipes make removing the MAP sensor impossible without removing the boost pipe. Quite possibly the position of the MAP sensor and the boost pipe were designed first and the AC unit was designed later. The MAP sensor position on the later revisions of the engine (accessible by just removing the engine under-tray) makes much more sense.

Here's my guide on how to access the MAP sensor on a CBBB engine:

1. Remove the engine under-tray
2. Remove the air intake housing (parts 17, 18, 20 and 21) - this will allow the removal of the radiator fan shroud
3. Remove the radiator fan shroud. Undo the wire connector first, then the 4 bolts. Gently remove the fan shroud through the top of the engine
4. Loosen the clips marked as red #1 and #2. Once those are loosened, you should be able to remove the rubber hose #3. It will be difficult, start with disconnecting from the part that clip #1 was holding, Putting it back on afterwards will be just as difficult
5. Under the engine, loosen the clip 6 and disconnect the rubber hose from the plastic charge air pipe. Prepare a cloth as you might have a tiny bit of oil drip out.
6. Under the engine, undo the plastic hose clip marked as the red #4.
7. Under the engine, undo the screw (bolt) labelled as the red #5. The AC belt will be in the way somewhat. Confirm that this is a Torx T30 screw, this is very important for the next step.
8. Under the engine, try to undo screw labelled as #6. This should also be a T30 screw, but it is very awkward to access and you will need a lot of strength to undo that screw. Make sure the T30 end is in the screw as much as possible, to reduce the risk of stripping the screw/bolt.
9. You should now be able to gently remove the charge (boost) pipe under the engine, with the MAP sensor still attached. The loom should have just enough slack to allow you to pull the pipe out enough to disconnect the sensor.
10. With the sensor disconnected, you can now either replace the sensor or do some continuity testing. Putting everything back together is pretty much in reverse order.

Hats off to you for actually coming back to say it's fixed and to actually provide some details for anyone else that has the same issue!

Kudos to you for taking the time.

Nice one.

Looks like that stiff bit of convoluted conduit intended to protect those wires has had exactly the opposite effect at the point they exit from it!