Oil Pressure Drops When Braking - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 07-22-2009, 08:01 PM
skewba98z28 skewba98z28 is offline
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Oil Pressure Drops When Braking

My I6 02 4x4 Trailblazer has started to drop oil pressure under hard braking and will stay at 0 until I give it alittle gas. After I give it alittle gas it will come right back up to normal. It seems I have to be braking pretty hard and the engine has to be warm for it to do it. Also it will not drop until it comes to a complete stop after braking hard. All other times while driving it acts perfectly normal. I've put around 4k miles on it since i've owned it and just did my 2nd oil change to it. I've put 5w 30 Valveline Max Life in it both times and it's at 121k miles now. Also when the pressure gauge drops it doesn't knock or make any kind of noise's what so ever. Any thoughts on what this might be or steps to take to get this resolved?
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  #2  
Old 07-22-2009, 08:08 PM
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chevtrlblzr chevtrlblzr is offline
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I don't know other than the obvious.
Are you sure it has enough oil in it?
Are you sure it's the correct dip stick.
How much does it take to refill when changing?
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Old 07-22-2009, 08:15 PM
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Keep in mind that we do NOT have a true oil pressure sensor. Our sensor either reads pressure or it doesn't, the needle movement is simulated based upon the RPM that resulted in the oil pressure switch finding over 5 psi (approx), the threshold for turning on the check engine light.

This may be an issue with the cluster itself or a bad pressure switch. I would suggest connecting an OBDII scanner and see what the PCM is actually reporting to narrow it down. If the scanner sees pressure and the needle is at 0, you have a bad instrument cluster. If it momentarily shows 0 psi, you may have a bad switch.....but this should also cause 'Low Oil Pressure' to display in the DIC (if equipped) and/or the oil can light on the dash to illuminate. - You didn't mention either, so I'm thinking a bad cluster.
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Old 07-23-2009, 02:51 AM
skewba98z28 skewba98z28 is offline
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It does display low oil pressure and when it hits zero it will say stop engine. Like I said this will happen for a split second and then it will go back to normal or when I tap the gas it will rise to normal. I'm going to have my local parts house order the switch tomorrow and replace it this weekend. Hopefully that will solve the issue. Sucks I just changed the oil last thursday to rule out oil issues. Guess it will be coming out unless I want it all over me. I'll be sure to keep the thread updated.
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Old 07-23-2009, 03:04 AM
WOOLUF1952 WOOLUF1952 is offline
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The oil pressure sending unit is on the side of the oil filter housing. You won't have to drain the oil. The oil level sensor is in the side of the pan and requires draining.
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