W210 ACC diagnostic codes and values

[rmasteller]

I think the ACC in my 1997 E300D functions fine, but is just low on refrigerant. So to analyze things a bit I thought I would check error codes and real-time values. I know there's a ACC button sequence to perform a flap control test, I'll do that soon.

I got in my car after work a few days ago and before starting the car, used the procedure to find the error codes.

Eb1231 - ETC sensor (B11/4)
Eb1235 - Emissions sensor (B31)
Eb1422 - Series interface (K1) connection to instrument cluster (A1)
Eb1459 - Series interface (K2) connection to instrument cluster (A1)

I cleared the codes and now several days later they have not returned.

Then I looked at my actual values, 4 times.
- Before I started the car.
- After I drove home and tuned the car off.
- (so two non-running measurements)
- A couple days later I took measurements driving to work.
- I then took measurements driving home that same day.
- (so two running measurements)

These are the measurements over those 4 samples. Do you see anything unusual? Might I just need my refrigerant refilled to get better cooling in the cabin? Setting it to 68/68 on auto just doesn't seem very cool on days in the 80F range.

1.In-car air temperature sensor: 37, 25, 22, 17
2.Outside air temperature: 28, 29, 25, 26
3.Left heater core temperature: 32, 61, 08, 07
4.Right heater core temperature: 32, 37, 07, 05
5.Evaporator temperature sensor: 55, 51, 48, 47
6.ECT sensor (DFI, IFI): 39, 92, 78, 83
7.Refrigerant Pressure in bar: 06, 12, 08, 09
8.Refrigerant Temp Sensor (F): 29, 46, 26, 29
9.Not Used (but has numbers?): 05, 05, 15, 16
10.Blower control voltage: 4.5, 2.1, 1.8, 4.5
11.Emissions Sensor (voltage): 4.3, 3.9, 4.0, 3.7
12.Sun sensor (voltage): 3.6, 4.0, 2.9, 3.8
20.Aux. fan control current (amps): 0.0, 0.0, 0.0, 0.0
21.Engine speed (x100=rpm): 00, 00, 16, 18
22.Vehicle speed (km/h): 00, 00, 35, 73
23.Terminal 58d (%Battery Volts): 00, 100, 00, 00
24.Battery Voltage: 11.5, 11.5, 12.7, 12.7
40.Software Status: 71, 71, 71, 71
41.Hardware Status: 36, 36, 36, 36
42.Unlisted/Unknown: 72, 72, 72, 72
43.Unlisted/Unknown: 136, 136, 136, 136

Thanks everyone!

[97 SL320]

Wow, thanks for posting code descriptions and other data. Many others post a string of code numbers and say " fix my car for me " then sometimes get irate when asked to take an active role in fixing their car by doing some research.

Eb1235 - Emissions sensor (B31) looks at outside air quality. Do a quick search on this site as someone else had an issue with this.

Eb1231 - ETC sensor (B11/4) looks to be Engine coolant temperature sensor. Do a code scan of the engine computer, this code might have originated from there. Given the 6.ECT sensor data values, things look OK.

7.Refrigerant Pressure in bar: 06, 12, 08, 09 looks OK based on what I remember from my 97 SL320 and 97 C280. I'd install pressure gauges on both sides of the AC system. You might have a stuck expansion valve that is limiting freon flow / worn AC compressor.

3.Left heater core temperature: 32, 61, 08, 07 4.Right heater core temperature: 32, 37, 07, 05 This shows that the heater valve isn't stuck open while driving. Be aware that the heater valve defaults to open when power to the valve is dropped, this is why the engine off heater core temps rise.

Have you checked the cabin air filter?

[rmasteller]

I've researched this some and read the threads where data is limited and further troubleshooting doesn't happen.

I replaced my behind-glovebox cabin air filters and the under-dash carbon air filters about 18 months ago. I have to park this car outside, so I have had some mouse nest issues in the engine bay, so maybe there's a pile of junk on top of those cabin filters again. I'll check.

I don't have any AC gauges. Maybe I should invest?

[rmasteller]

No problems with the cabin air filters - just a few small locust tree leaves and stuff. See pics.

I have a thermometer to put into the dash vents, I'll do that today since it will be in the 80's here.

I should also go through the flap test procedure.

To confirm, the amount of refrigerant pressure doesn't seem low?

[97 SL320]

An AC gauge set is needed to further diagnose though there is one test you can do.

With the AC running, feel the discharge side of the evaporator ( this leads to the suction side of the compressor ) . This should be cold to the point you get condensation on a humid day. If cold, you have a problem in the air flow system in the car. If warm, there is a low freon charge / worn compressor / expansion valve nearly stuck shut.

[rmasteller]

With an 80 degree day, and the ACC set on auto at 68, the thermometer placed in my central dash vent read around 45 all the way to work. And, the car was fairly comfortable and the air flow out the dash vents was fairly strong on speed 4 (out of 7?). In the past I've manually set the fan to max to get some adequate flow out the dash vents. Could simply knocking the small amount of loose stuff off the cabin air filters have made that much difference in air flow? Maybe everything is fine? No failure codes have returned in the ACC.