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Marty, European Car Expert
Category: UK Car
Satisfied Customers: 406
Experience:  ASE & Bosch Certified Master Tech. Over 30 years experience.
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How can I check to see if the optical sensor is working on

Customer Question

How can I check to see if the optical sensor is working on my Chevy 6.5 td.
JA: Which sensor are you asking about? O2? MAP? Did any codes pop up? What is the model/year of your Chevy?
Customer: The model is a Tiffin Allegro RV built 1998. No codes have posed up on my reader. I believe its called the Injection pump optical sensor
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Im based in the UK and we are looking fix it our self. We have tried a new PMD with heat sink and a relocated wiring loom. We have power to the fuel solenoid
JA: Anything else you think the mechanic should know?
Customer: We believe we have lift pump pressure and a return to the tank
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Chevy Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: UK Car
Customer: replied 1 year ago.
When you say fill out the form is that the credit card form for payment you are refering to
Expert:  Technicaldan replied 1 year ago.

Hello, I will try to help you, although I'm in the UK also so I am relying on research and data.

What is the actual issue, i'm guessing a non start but it would be good to clarify and what have you tried so far.

Code P0251 would usually be stored if there is a fault related to the pump optical sensor.

The engine would still run with a failed sensor, albeit in reduced power mode.

When it comes to the optical sensor and the DTC P0251, one possible cause is the optical sensor filter harness.

These are well known to fail. Follow the harness coming out of the optical sensor and the filter harness will look like a little box added in to the wiring, the plugs match up so just unplug it and plug straight to the sensor.

As you're question specifically was about how to test the optical sensor, I have obtained you the information on how to troubleshoot the dtc P0251, like you asked, I also do try to be helpful and am happy to continue a little further usually than the specified question of it helps.

Let me know whats what and if the procedure helps, if the engine doesn't run, on the Hz test you won't reach 900 rpm or 60 hz, I would expect to see 30 or 40hz at cranking, I think it referred to j and a number, a multimeter that can measure frequency will do.

Expert:  Technicaldan replied 1 year ago.

I know the data is for not for a RV, but for a chevy 6.5td, I have various options if something doesn't match.

Customer: replied 1 year ago.
Do you have a general Chevy 6.5 TD wiring diagram we are looking to trace the source of power from and to the PMD, fuel solenoid, optical sensor ans any other associated relays. The vehicle was parked up before Xmas 2015? When I came back to the vehicle in Feb it wouldn't start. We have tried a new PMD and wiring harness to the pump. We are trying to eliminate various elements of the system.