P0521

[wedge1]

I got the CEL this morning. My code reader says P0521. The service manual doesn't have this code, but it does have P0522 ad P0523 which seem to be related. The instrument panel gauge is reading at the maximum pressure reading. I checked the oil level. It is midway between "add" and "full". If this were the "good old days", I would just change the oil pressure sending unit and be done. I'm tempted to do that and hope, so I wish that I knew where the sending unit is. So, two questions:

1. Is changing the sending unit likely to fix it?

2. Where is the sending unit?

It's a 5.3L and I have 171,000+ miles on it.

Thanks. Wedge1

 

[Texan]

Read this thread all the way to the bottom.

Engine code p0521 - Ask the GM Technician - GM-Trucks.com

 

[wedge1]

Hi Texan,

Where are these items located? Is this on top of the engine near the back? I've heard rumors about needing to take off the intake manifold to get to them. Is this true? The engine is a 5.3L on a 2005 Trailblazer. I assume that the part #706 is the sending unit.

When I turn the ignition key to run, the oil pressure gauge on the instrument panel goes to about 50. As I am starting the engine, the gauge drops to 0. When the engine is running, the gauge goes to the full maximum reading (right side). Is this any help?

Thanks. Wedge1

 

[Texan]

The sending unit and that little filter are on the exterior of the intake manifold
on the drivers side at the back of the engine. My TB is a I6, so I can not talk
about this from experience. A new sending unit may fix your gauge problem.
I think that the little filter is used for the V8's that have the 4,6,8 (DOD) system
used for fuel mileage improvement.

 

[C-ya]

The link above has a picture of where the filter and the sending unit. Parts 706 and 452, I believe.

Oh, and the DOD/AFM engines have 4 or 8 cylinder modes, not like the Caddy (Northstar?) engine that was 4, 6 or 8.

 

[Texan]

Here is another link that may help, and is where my first link came from.

http://gmtnation.com/f26/low-oil-pressure-please-help-9755/

 

[C-ya]

Don't read this thread. It'll scare the bejeesus outta a 5.3 AFM owner. Another 5.3 with AFM bites the dust ~ Chevrolet Active Fuel Management Problems

Gotta get my AFM turned off ASAP!

 

[{tpc}]

Do all the 8 cylinder Trailblazers/Envoys have AFM? Because they are 5.3? Or how do you tell?

 

[strat81]

Do all the 8 cylinder Trailblazers/Envoys have AFM? Because they are 5.3? Or how do you tell?

2003 and 2004 GMT360s had the GenIII LM4 5.3 which did not have DOD/AFM.

2005 and newer GMT360s had the GenIV LH6 5.3 which did have DOD/AFM.

 

[{tpc}]

2003 and 2004 GMT360s had the GenIII LM4 5.3 which did not have DOD/AFM.

2005 and newer GMT360s had the GenIV LH6 5.3 which did have DOD/AFM.

Thank you for the information.

 

[wedge1]

So here is how this turned out. I decided to just change the sending unit and see what would happen. I could barely get my hand onto it. I also would have needed to buy a deep-well socket. (It would have been a good excuse to do it.) But, I took it to a local shop, and they diagnosed that it needed a new sending unit. They changed it, and everything is working great. I'm just $400+ lighter. I should have tried a little harder.

Thanks to all who responded. I do have one more question. The tech told me that, if the oil pressure were too low, it would cut off the electricity to the fuel pump under the assumption that there was an accident. This doesn't seem logical to me. After all, the pressure is low, zero, when I'm starting it. Does anyone know if this is true? Thanks. Wedge1

 

[The_Roadie]

...The tech told me that, if the oil pressure were too low, it would cut off the electricity to the fuel pump under the assumption that there was an accident. ...

Perhaps other vehicles he's familiar with. Not this platform, that I'm aware of. People have failed oil pressure switches and the engine doesn't cut out on them.

I might believe the airbag rollover sensor that deploys late-model side curtain airbags might also cut off the fuel pump, but I don't have that system in my vehicle or the 2004 shop manual so I can't check it out.

 

[C-ya]

Just got the code today and my oil pressure gauge is pegged at full pressure when the key is on/vehicle is running. Torque is showing 128.9 psi. I'm trying to find out if it is covered under my aftermarket warranty.

I think I'll hook an analog gauge to it to verify the pressure and then just take it in once I find out if it is covered. I hate being at their mercy when they say it's not covered then I owe them for the diagnosis.

 

[C-ya]

Well, didn't find a gauge, and I also found out it wasn't covered under the warranty (??). So, I took the chance on it being the sending unit, and $50 and 20 minutes later, I have a functioning gauge on my dash.

 

[CajunWon]

Can u get verification of the part#s for my 2006 Envoy 5.3?

12677836 sensor

917-143 Engine Oil Pressure Sensor Filter

I'm out of town, need to have parts ready

Thoughts on driving with this cel? After checking dip stick but without pressure test?

 

[Mooseman]

Checked on RA and those seem to be the right numbers.

 

[CajunWon]

I'm 1,000 miles and couple weeks away from truck. Oil at proper level. Gauge pegged at 80. I'm thinking OK to drive, just not far from home. I'll give her a towing phone#.
Guessing sensor is bad but will order screen so don't have to wrench on it twice.

 

[Mooseman]

That's the way it usually fails. When the screen is clogged, the pressure shows low. If your pressure was fine before it pegged and there's no noise, I'd be confident that the pressure is fine.

Oddly enough, it's actually easier to get to that sensor on these trucks compared to the full size trucks. Just disconnect the brake booster hose from the booster and swing it out of the way. I used a 21 or 22mm 12 point socket to get it out although the last time I had to use an actual sensor socket on the Avalanche.

 

[CajunWon]

Got back home to replace this sensor.
Just disconnected the booster for a little room. Was able to reach around both sides, but very tight. The special socket is a must have imo, sure don't want to strip the corners. Took about an hour, mostly from over complicating the connector.
Couldn't get the screen out, so took a chance on doing this again.

Had trouble clearing the mil and code (many attempts til it worked), but the gauge and torque pro now show varying pressure.