Check engine light codes 4 and 9
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Joined: Apr 2009
Posts: 18
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E55
Check engine light codes 4 and 9
Having some issues with my 95 e320 with 132k miles. Read the code and came up with 4 and 9.
This is what I have found so far:
4 Air injection system faulty hot film mass air flow sensor with hot wire
9 Intake air temperature sensor, open circuit
Can someone make a recommendation as to where to start a diagnosis please.
Issues that I have with the car are: hard starts when warmed up. When cold, one touch and starts right up. When hot, keeps cranking and have to push the gas once or twice to get it started. Also seems to have lack of power under 4k rpm. Seems sluggish at low rpms and all of a sudden picks up power after 4K.
Thank you in advance for the support.
This is what I have found so far:
4 Air injection system faulty hot film mass air flow sensor with hot wire
9 Intake air temperature sensor, open circuit
Can someone make a recommendation as to where to start a diagnosis please.
Issues that I have with the car are: hard starts when warmed up. When cold, one touch and starts right up. When hot, keeps cranking and have to push the gas once or twice to get it started. Also seems to have lack of power under 4k rpm. Seems sluggish at low rpms and all of a sudden picks up power after 4K.
Thank you in advance for the support.
MBWorld Fanatic!
Joined: Nov 2002
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From: Massachusetts
2018 GLE350, 2014 G550, 2000 SL500, 1980 TR8, 1995 E320 Cabriolet
While possible, the odds are against both of these codes appearing simultaneously because they involve two different sensors (albeit, two that are located close to each other). I ask this question often - what condition is the wiring harness in? Your car is in the problematic range of years and if the harness has not been replaced, it is most certainly degrading. Inspect the condition of the wires leading to the connectors for each of these sensors before investing in new ones. If the insulation is cracked/frayed, it's more likely that the harness is shorting out the signals from the sensors than it is to have both sensors fail. Easy and cheap to check first (but expensive to fix).
Thread Starter
Junior Member
Joined: Apr 2009
Posts: 18
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E55
I checked the harness. Looks pretty new. The connectors are not brittle and the tape around the harness is flexable and not discolored. I picked up the car with 114k miles last year and the previous owner had done some service already. They may have already replaced the harness. I did do some service work last weekend, cleaned the MAF and temp sensor with electronic parts cleaner. Also changed the fuel filter. This morning, the check engine light was off for about 5 miles and came back. The idle is smoother with the new filter.
