2009 - GL550 - P0172 & P0175
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From: Southern New Hampshire - USA
CLS550 - Launch Edition | GL550
2009 - GL550 - P0172 & P0175
Backstory: Recently driving our GL and I started to notice some oddities in the engine performance and sound. Shortly thereafter and, fortunately, close to home, the battery light came on and I lost power steering suddenly. Sure enough, after limping the car home, I found the upper right engine pulley and serpentine belt had failed. There were pieces of belt and bits of black plastic from the pulley around the engine bay, but not a huge amount.
I replaced the pulley and belt, along with both air filters. However, upon the first start of the car, post belt/pulley replacement, the CEL was now on. The performance (normal driving) seems fine. However, the idle is occasionally rough. The CEL codes are P0172 and P0175, "running too rich" on both banks. Whereas this issue was seemingly a result of the belt/pulley problem, I'm confused what could be causing this mixture issue. Are these related? I've cleaned the MAF, changed the air filters, and visually inspected the intakes (plastic), which seem undamaged from the belt/pully failure. I can't find any evidence of damage from the incident, but it's too coincidental that it could be unrealted. I tinkered with my diagnostic tool, which allows me to adjust the lean/rich mixture levels, but it didn't seem to change the idle roughness or resolve the CEL.
Does anyone have any thoughts on what to try next? I've read elsewhere that I could try replacing the purge valve, but haven't done that yet. Any insight, tips, or troubleshooting is so greatly appreciated. I'm currently frustrated and at a loss of where to look next for a culprit.
I replaced the pulley and belt, along with both air filters. However, upon the first start of the car, post belt/pulley replacement, the CEL was now on. The performance (normal driving) seems fine. However, the idle is occasionally rough. The CEL codes are P0172 and P0175, "running too rich" on both banks. Whereas this issue was seemingly a result of the belt/pulley problem, I'm confused what could be causing this mixture issue. Are these related? I've cleaned the MAF, changed the air filters, and visually inspected the intakes (plastic), which seem undamaged from the belt/pully failure. I can't find any evidence of damage from the incident, but it's too coincidental that it could be unrealted. I tinkered with my diagnostic tool, which allows me to adjust the lean/rich mixture levels, but it didn't seem to change the idle roughness or resolve the CEL.
Does anyone have any thoughts on what to try next? I've read elsewhere that I could try replacing the purge valve, but haven't done that yet. Any insight, tips, or troubleshooting is so greatly appreciated. I'm currently frustrated and at a loss of where to look next for a culprit.
Last edited by cnpdmb11; Feb 13, 2025 at 11:25 AM.
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From: NE OHIO
1998 SL500,2011 GL550,2009 ML350,past 1995 E320 Cabrio ,2005 ML500,2006 ML500,1996 SL500,1972 280SEL
possibilities
Have you checked for any vacuum hose or leaks from the belt parts flying around in the engine compartment?
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NGL450 w/EORP, S550
There aren’t a lot of vacuum connections on the m273 but the ones that could be affected are on the front of the engine servicing the vacuum actuator or the intake manifold, among others.
also check that the shredded belt didn’t damage any electrical connectors.
also check that the shredded belt didn’t damage any electrical connectors.
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From: Melbourne, Australia
2010 ML550 VIN WDC1641722A564750, 2010 B180
A systematic check of all connectors and vacuum hoses won't hurt. As you've got both banks reporting the same issue, look to the common systems and I'd start with your MAF sensor - check the connector and make sure the wiring is good and that its actually in far enough without obstruction. That was the obvious last thing that was touched. You might have a pin that's bent or similar. After that check the inlet manifold actuators and all hoses and make sure your air box is on properly and the hose from the air pump is connected.
Do the codes appear when the car is cold v hot? Try clearing the codes when the engine is at operating temperature and see if they return when its hot. Could be the air pump so check connectors there too.
Check also the PCV rebreather pipe that runs from the back of the RHS cylinder head to the throttle body. It could have become dislodged. Check also the throttle body to make sure its clear after you.removed the MAF - who knows it might be stuck.
Hope this gives you some ideas.
Do the codes appear when the car is cold v hot? Try clearing the codes when the engine is at operating temperature and see if they return when its hot. Could be the air pump so check connectors there too.
Check also the PCV rebreather pipe that runs from the back of the RHS cylinder head to the throttle body. It could have become dislodged. Check also the throttle body to make sure its clear after you.removed the MAF - who knows it might be stuck.
Hope this gives you some ideas.
Last edited by BlackML550; Feb 14, 2025 at 03:48 AM.
