My CDI starting throwing a 2025-1 two weeks ago, which my Foxwell says is

Check Component B28/5 (pressure sensor downstream of air cleaner). The signal voltage is too high.


I swapped out my MAP sensor (that is B28/5 according to the WIS) and still received the code. I then tested the MAF wires, I am getting 5V and 12v from 3 and 5 respectively which is correct.

So I opt for a new MAF, the whole housing, MAP and MAF sensors on it. Replaced that last night, cleared the codes, started it up and it threw it immediately.

Any idea where to look next? The WIS doesn't give you places to look for diagnostics. I am wondering if there is a vacuum leak somewhere.

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2005 E320 CDI - 101K

Signal voltage too high means that the sensor isn't changing state or signal is beyond the expected limit. Put a volt meter on the signal line when everything is connected then apply vacuum / low pressure. It is possible to have a power wire pinched to the signal wire.

You also need to look at where the is sensor gets pressure from, maybe there is a broken or clogged hose.

A MAP sensor has a ground , 5 V voltage supply and a signal out. Systems generally use 0.5 V as the floor and 4.5 V as the limit of signal range. If the computer sees voltage beyond these limits it will trigger a low / high code.

Also, have a look at live data though be aware that some systems will substitute in an expected value when a component fails so an actual volt meter on the wire is always a good test.

Update, below is what I have done to date.

1- replaced MAP sensor
2- replaced entire MAF, which includes the MAP sensor
3- replaced the charge air temperature sensor which is the clip shape sensor on the lower part of the left side charge air tube

All parts are OEM. I am still getting the error.

Accordingly to the diagnostics, the Boost pressure, Atmospheric pressure and Intake Air pressure should all be within 30 hPa. I measured mine, they are below

boost- 976
atmospheric -990
intake air- 790

So what measures the intake air? I thought it would have been the MAP or charge air but that didn't change anything. The only sensor I have not changed is the charge pressure/turbo boost sensor as they call it. This is the one on the left side of the intake near the top, but since the boost is good I am not inclined to change it. Also the wires look good with no crimps.

Also, can someone with a 05/06 CDI read their measurements and report back?



@97- where do you put on the voltmeter when it is hooked up? I don't see how to do this without splicing the wire which I don't wan to do. The sensor it is complaining about is the MAP sensor.

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2005 E320 CDI - 101K

How many miles are on it?

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Jim

136K

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2005 E320 CDI - 101K

I'm wondering if you are seeing exhaust back pressure that is higher than it is supposed to be - plugged exhaust part? Is the car predominately used on short trips? What kind of oil have you been using in it?

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Jim

Some short 10 mile round trips, but mostly 30-60 mile round trips. I use Total, blackstone reports are excellent.

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2005 E320 CDI - 101K

I'd look closely at the exhaust system from the turbo back. Does it use oil?

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Jim

High map sensor voltage that doesn't change could indicate an open in the signal wiring.

Unplug MAP, measure voltage directly at the connector.

If you see 0V it's open.

If it's still at 5V then it is a ECU/Module control problem.

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1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.

Good point. I recently had a BMW in that a mouse had eaten through the O2 sensor wiring.

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Jim