I have a '95 E320 wagon with 146K. The check engine light just came on and I'm getting a code 4 from the diagnostic module ==> Air injection system faulty hot film mass air flow sensor with hot wire

Two days before the light came on I replaced the air filter and switch-over valves for the EGR and air pump. I've reset the code twice so far and no other codes are being stored. I haven't read codes from any other modules yet.

Should I assume the MAF is faulty or can it be cleaned and/or tested?

__________________
Glen Tokuhara
Beauty & the Beast and the wagon that could!

You want to first check that you have the correct hoses on the SOVs . I see some that get reversed when they change the 2 SOVs....
Same for the plug....
I would then clear the DM, take it for a 5 min ride and go right to HFM module [ pin8] before DM registers another CE lamp.
Make sure #8 memory is clear first , too.. That will register a code #1 to let you know it is...
Also, check that all hose connections on cross-over intake pipe have been fastened and AIT sensor is back in place

Thanks Arthur. I'll check it out and report back.

__________________
Glen Tokuhara
Beauty & the Beast and the wagon that could!

Ok...had time to check things out yesterday.

The CEL has NOT illuminated for since Thursday, however, the DM had a stored code 4.

Pin 8 reported a single blink on the tester; no stored faults.

Interestingly, pin 14 (CC/ISC) reported codes:
5; Stop lamp switch
11; Fuel safety shut-off to LH-SFI control module

I reset the DM and CC/ISC modules, drove the car around for a few minutes; no stored faults.

Drove it again last night and this morning still no stored faults.

I'll run it through as many start cycles as I can today and see what shows up.

I checked the SOV connections...looks ok. Is there a way I can verify which electrical connector goes to which SOV? I'm pretty sure I got 'em right, but ya never know! ;-)

Thanks!

__________________
Glen Tokuhara
Beauty & the Beast and the wagon that could!

SOVs
Air [y32]....br & gy/bu
Egr [y27]..bk/r & gy/wt

This is what I would check
1-is AP running??? [ runs for a min after cold start, only between 10-40C]
SOV is wired in parallell w/pump., so if pump comes on , sov should also have power.
Easy check is to look for vac at line coming out of SOV when AP is running..
If vac there , you could have a bad AIR shut-off valve [ which is actuated via line from SOV, or check valve downstream. [ crud sticking prolem]

Remember , for the ECU to bring up an AIR code , it relies on a very low voltage [ .02-.04v] lean reading from the 02 sensor when it does a self test.. sometime there is nothing wrong with AIR system, but rather a not so sensitive 02 sensor...
A little tricky diagnosis here.. )
But don't go there til you have verified pump is running [ if not , there is an electrical prob w/fuse or K17 relay.
Check pump first...............

Ok...the electrical connections to the SOVs are correct.

I haven't been able to verify if the AP is running yet though. Seems, whenever I have a chance to look at the car, it's warm. Hopefully, this weekend.

Otherwise though, the CEL has not come on, however, there is a stored code=4 in the DM which I haven't cleared. No other stored faults in any modules.

__________________
Glen Tokuhara
Beauty & the Beast and the wagon that could!