Charge Pump?

[emerydc8]

Can anyone tell me if the small pump under the brake master cylinder is the charge pump? What does this pump do and when should it be running? Thanks.

 

[gsxr]

According to the FSM job 42-0818, the small pump under the MC is the "ASR pressurizing pump (M15)".

The function is described in 42-0800 on page 10 under the "Hydraulics" subheading, also pages 31-32 and 37.

 

[emerydc8]

Thanks, Dave. But I have to admit that I don't know if I have an FSM. Is that the two CD's in the Service Manual Library?

 

[gsxr]

Thanks, Dave. But I have to admit that I don't know if I have an FSM. Is that the two CD's in the Service Manual Library?

Yes - FSM = Factory Service Manual, the two CD's. Also online at this link, click M119, then click Group 42.

 

[emerydc8]

Thanks!

 

[Trae]

Jon, let me know if your attempt is successful with code #21 on pin 6. I have not had time to deal with it yet.

 

[emerydc8]

Will do, Trae. I was hoping that the tiny electric pump under the master cylinder was called the charging pump. If it was, I was going to replace it because it didn't look like a big job. Unfortunately, like Dave said, the tiny pump is the ASR pressurizing pump. I think the charging pump is integral to that big ASR unit and I'm not in any hurry to tear into that one. I have been clearing code 21 from pin 6 for years with no apparent effect on the braking. What I did not have was a code 24 on pin 6, which I cleared last week. This is the ASR charging pump (M15). So, I'm not sure if the code 21 and code 24 are related. I might just wait to see if code 24 shows up again a few times.

Code 21 on pin 6 has been one of just four recurring (nuisance) warnings for several years. The other three--transmission overload protection switch does not close, air injection inop (I unplugged it when it started making a grinding noise), and module box overtemp, are all on the Deferred Maintenance Item list. I may get to them someday.

 

[Trae]

I had the exact same codes: air injection inop, module box overtemp. But they have not recurred.

 

[samiam44]

Emercy,


You might consider replacing the 'transmission overload protection switch". I bet it's weeping oil at this time too- and I was getting intermidant engine missing at times- all is better with the new switch. ~$75 with necessary o-rings. I've done them on both my 500e and 420e. Later was done due to leaking before the code appeared. I think after a while trans fluid contaminates the switch and you get the failure to close error.

over temp is *always* on my cars, but I live in Texas. I think Dave pointed me to where MB removed the ECU/CANS fan in 95? or 96.

Michael

 

[emerydc8]

I don't think it's leaking there but my transmission has been leaking for a few years from another place. I may put the overload switch on my list of things to do soon.

 

[Trae]

Did not have the dreaded transmission overload protection switch code yet.

 

[gerryvz]

Module box over-temp codes are nothing to worry about. Clear them when you come across them, otherwise nothing to be concerned about.

Cheers,
Gerry