The Dreaded P0171

MAF Wires and plug look ok? Maybe clean and inspect?

How many miles and what other kind of maintenance over its lifespan?

 

Have you looked at fuel delivery? Fuel pump, injectors? Found an interesting video which diagnoses it in a Prius. Could be something to check.

 

If you have the ability, I'd perform the same test to see the waveform of the pump. That'll help eliminate the possibility of just blindly throwing parts (and money) at the problem. Good luck with this and post back what the fix is.

 

Sure would be cool if we had some images or videos of the healthy wave form of various parts that fail on a Prius... That'd be an awesome resource. And for that matter, what's the least expensive way to get a scope that can do this?

 

There are pumps that fancy in a Prius, but I don't think the fuel pump is one of them. I think it just has power and ground; it's on or it's off.

 

I have a Hantek 6022BE and find it quite useful. I use it with the same laptop that I have Techstream on. I got mine from Amazon.

 

Found this video which breaks down testing on a lean running Prius engine. Thought it was quite informative.

 

True in one aspect. I believe that since this is a brushless motor, it is commanded "on/off" by pulse code modulation. It is switching DC currents to the windings thereby causing the rotor to turn due to the expanding/collapsing magnetic fields. The waveform, taken from a current probe attached to one of the power leads on the pump gives an indication of the expand/collapse of the magnetic field within the motor.

While watching the first video, I spotted the current probe attached to the fuel pump and knew exactly what the Tech was looking at.

 

I don't think so:



Simple relay that applies 12 volts across the motor.

There are other things in the car (engine water pump, inverter pump) that have separate connections for 12 V power and a pulse train input to set the speed. Not this one.

It probably does have an interesting current waveform, as any motor would, just from the commutation happening inside it (whether that is done electronically or with brushes). That said, you're probably on your own to interpret that waveform, as it isn't one that Toyota mentions in their troubleshooting. They just have you check the motor's resistance, and whether it pumps when 12 volts are applied.



The fact that a resistance is specified suggests to me that it is a conventional motor with brushes. An electronically-commutated one typically doesn't look much like a simple resistance across the terminals (you'd be trying to measure the 'resistance' of some active electronic circuit).

 

Here's some Repair Manual excerpts. If they're pointing to other pages let me know; I'll try to find them.

 

I stand corrected.

Without a manual nor any true experience with these cars (I've only had mine since March) I had to make some assumptions. I always enjoy reading your posts on the various topics here as I always learn something. I appreciate the detailed explanations.

Still, I am curious as to the vast difference in the waveform's in the one video. Time for a bit more reading and learning.

Thanks for posting these. I need to find a manual somewhere for my 3rd Gen.

 

Awesome! Glad to hear you got it running again! Thanks for posting the follow-up. It'll help others down the road.

 

So did replacing fuel pump solve p0171 permanently?

 

There's so much quality info in this post, I figured I'd reply here rather than start a new one. I assume I have a vacuum leak, but given the above info, maybe there's an issue on the fuel side leading to P0171. I did the EGR service and spark plugs 1000 miles ago and now it's throwing this code on the second sub-freezing morning at idle. The most likely scenario is that I didn't put a hose clamp back properly and there's a vacuum leak. It's 7 weeks to get an appointment. Any other ideas to try first? STFT is better at high RPM, worse at or around idle.

 

It didn’t for me. Still trying to figure this out.