[amosfella]

The car is throwing a strange code, but as far as I can tell, the live sensor data doesn't fit the code. I get a code P0102, MAF low voltage, but when I turn on the live data, I get readings at idle of twice the amount of air going into the engine than is normal. I get readings of 10.3-10.7g/sec. From what I've been able to find out, it should be reading half of that to be normal.

I may misunderstand how the MAF works, but I thought that the voltage increases as the airflow increases. So, if the voltage is low, how can it be reading so high??

I have a STAR system inbound, but for now, I have a Autel 500 series reader.

Any ideas??

Thanks in advance.

 

[mrboca]

Unplug the MAF connector and plug it back. If the MAF gives a consistent low output to the ECU, how is the ECU going to provide the proper air/fuel ratio ?

What you read is probably the substitute value from a table stored in the ECU, in case the MAF fails.

 

[amosfella]

Unplug the MAF connector and plug it back. If the MAF gives a consistent low output to the ECU, how is the ECU going to provide the proper air/fuel ratio ?

What you read is probably the substitute value from a table stored in the ECU, in case the MAF fails.

Ok. I didn't know that such a table existed in the ECU. But wouldn't the readings remain fairly steady if it was reading from a table??

 

[mrboca]

It is mainly based on the throttle opening, so the ECU guesses the airflow intake, together with the coolant temp data, and incoming air temp data. If you take the connector out your car still runs, not as smooth and efficient, but runs, with a MAF malfunction code.

 

[amosfella]

ok, so I had the STAR system on it. in the live data tests, the voltage of the MAF never changed. It was 0.96x... Didn't change with any RPM change. The voltage to the leads in the wiring harness is good. I"m thinking that the sensor is bad.

Does disconnecting the MAF while it's running tend to throw a air temp sensor warning??

 

[mrboca]

With no airflow the voltage output should be 1V and with WOT it should read around 4.5V. So if there is no change, the MAF is likely bad (provided that the voltages supplied by the ECU are at the connector.

If you pull the sensor, the IAT sensor fault will come up, and the ECU will default to a low IAT reading by the ECU which will cause a rich fuel mixture.

 

[amosfella]

I did the harness 2-3 and 4-3 tests at the plug. One was 14v, and the other was 5.4v or something right around that number. So, I don't know if it's the harness. It wouldn't seem so. I found a good deal on a new genuine mercedes MAF. Less than the cheapest aftermarket I could find, so I ordered it.

Previous owner put K&N filters into it. I'm pretty sure that he over oiled them. The MAF in the car seems to be used, as it's marked in paint pen to be for a 99 ML500.

Should I clean out the air intake filter box before installing new filters and MAF? Would brake Kleen work for that??

 

[mrboca]

I have no experience with the K&N filters, but many say K&N and MAFs do not mix well, especially if over-oiled. Brake Kleen should be fine. Maybe you could try cleaning your MAF element with MAF cleaner or electronic contact cleaner. Small chance it may come back to life

Never use silicon based sprays, liquids under the hood. MAFs and O2 sensors do not like them.

The voltages are fine.

 

[amosfella]

So, today I put in the new MAF I got yesterday. I changed the air filters, and cleaned the air box out with brakecleen to make sure that there was no oil in it from the K&N filters. I cleared the codes, and started and ran the car a bit. CEL didn't return. Before, it would return on the second restart after clearing the code. So, we'll see if this works. I didn't have time to take readings to make sure that it was working fully right, but we'll see how things go.