DTC 56

[QB93Z]

Anyone know what this code is? Tech 1 says DTC 56 - Sec MDP sensor mulfunction. This is for a 1994 ZR-1.

[mike100]

I think it's the port throttle vacuum sensor for the secondaries fault.

as per google search for 94/95 LT5 code listing:

Secondary Air Inlet Valve Actuator Vacuum Sensor Circuit (Signal Voltage High “High Vacuum or Signal Voltage Low” (Low Vacuum)-The map sensor and hose under the ecm bracket.

I could verify when I get home as I still have a 95 Y-car FSM

[A26B]

MDP is the manifold differential pressure sensor which on a 94 model, is located under the plenum, immediately forward of the DIS module.

[secondchance]

Thanks guys. That posting was done by Jim on my behalf.
Anyone know where I can get this sensor at a reasonable price?

[secondchance]

http://www.ebay.com/itm/16231141-ACDelco-SENSOR-ASM-MDP-/270741954625?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item3f097a6041

Is this the correct part?

[A26B]

http://www.ebay.com/itm/16231141-ACDelco-SENSOR-ASM-MDP-/270741954625?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item3f097a6041

Is this the correct part?

Could the fault be a vacuum hose or elec connection? Pretty expensive sensor.

[secondchance]

Could the fault be a vacuum hose or elec connection? Pretty expensive sensor.
That is what she said - I meant Jim said!
After 124,000 miles I figured just replace once under.

[Aurora40]

That is what she said - I meant Jim said!
After 124,000 miles I figured just replace once under.

It's basically just a MAP sensor. They are pretty reliable. It measures the pressure to see if the secondary system is being activated. If you take the plenum off, I think you'd be remiss not to check all the vacuum lines and such to make sure the secondary system is in fact operating properly vs just replacing the sensor.

And Jim, don't you have that LT5 emissions training book? That thing has everything about every code you'd ever want to know! :)