Multiple sensor failures after carbon cleaning intake valves. Wire short?

[AVC]

In brief, yes, something shorting the 5v or 12 ref from the PCM can cause system wide issues.

Focus on the sensors with PERMANENT codes.

1. Unplug one of those sensors.
2. Do a "clear all codes", start (or attempt to start) engine and see which PERMANENT codes re-appear.

If the same 3 PERMANENT codes re-appear, plug that sensor back in, and repeat step #1 and #2 until only ONE permanent code appears.

Troubleshoot that sensor circuit/wiring/connector.

 

[Ven Zoah]

In brief, yes, something shorting the 5v or 12 ref from the PCM can cause system wide issues.

Focus on the sensors with PERMANENT codes.

1. Unplug one of those sensors.
2. Do a "clear all codes", start engine and see which PERMANENT codes re-appear.

If the same 3 PERMANENT codes re-appear, plug that sensor back in, and repeat step #1 and #2 until only ONE permanent code appears.

Troubleshoot that sensor circuit/wiring/connector.

Thanks for this tip! When I erase the codes, it erases everything except the three permanet codes.

And after I unplugged the three sensors and put the car in accesory mode again, I got the circuit high codes for those sensors even though they are unplugged. Is that normal?

 

[AVC]

Yes, if you unplug a sensor, you will get a circuit error; typically "circuit high".

Did you start the car after unplugging those sensors? Did all the rest of that long list of codes remain clear?

If you'd go back and perform the procedure I suggested, you can probably narrow it down to ONE of the 3 sensors that is causing the problems.

 

[edmaz]

The fact that your vehicle first stalled, and now will not start at all, IMO would either be an issue with the crank sensor signal, or the spill valve in the HPFP somehow became stuck closed (which IDK if is even possible to happen), resulting in fuel being blocked. I believe the crank sensor wiring is the prime suspect, and you could do a quick redneck test on a sparkplug to see if there's any spark while it cranks.

You wrote previously that you planned to unwrap the wiring harness. So if there's no spark, and you have those wires unwrapped and separated, it would be easy to inspect and test the 3 crank sensor wires, all the way from the crank sensor connector to the PCM connector.

Hopefully the problem is only one or more shorted wires in the bundle, which you can repair without a huge effort. However, there's one other possibility (that I don't even like to mention), which is a trashed PCM due to being backfed from a shorted wire. I certainly hope that's not the issue with your vehicle, and wish you a speedy and inexpensive resolution.

 

[AVC]

, which is a trashed PCM due to being backfed from a shorted wire.

I wouldn't suspect this as all the other pending codes went away after unplugging the three sensors, which at first blush, would hint that the 5v/12v PCM reference came back and the other sensors are working.

Don't know the PCM strategy for missing MAP, CKP and fuel pressure signals. A reasonable guess that the engine might not start with missing CKP, although many vehicles use stored calibration values and CMP signals in a pinch for limp mode, and may just have extended crank times; 5 sec or longer.

 

[edmaz]

I wouldn't suspect this as all the other pending codes went away after unplugging the three sensors, which at first blush, woul hint that the 5v/12v PMC reference came back and the other sensors are working. ...

You may very well be correct about what you wrote. My comment was intended to reflect the myriad possible events, when electricity flows through the circuits of a board in an unanticipated direction. So 'trashed' might actually be some small damage done to the crank sensor signal or vehicle start processing included on the board.

I certainly don't know if anything like that is possible or not, but quite a while ago I made it a rule to never eliminate anything, prior to testing, whenever electricity is involved.

 

[Ven Zoah]

Yes, if you unplug a sensor, you will get a circuit error; typically "circuit high".

Did you start the car after unplugging those sensors? Did all the rest of that long list of codes remain clear?

If you'd go back and perform the procedure I suggested, you can probably narrow it down to ONE of the 3 sensors that is causing the problems.

Ok something weird happened. I unplugged the three sensors (Crankshaft position sensor A, Manifold pressure sensor, Fuel rail pressure sensor A), cleared the codes and then attempted to start the car. It cranked for 3 seconds then actually started up for about 2 seconds then I shut it off.

Now there are 12 codes instead of 27.

I will plug in one sensor at a time and then clear codes and try to start again.

 

[Ven Zoah]

Updates on my testing:

• All 3 sensors unplugged - Able to start engine
• Fuel rail sensor plugged in only - Able to start, a little rough at first
• Fuel rail + Manifold pressure sensor (MAP) - Cranks, no start

 

[Ven Zoah]

Found this video that demonstrated what happens when the MAP sensor shorts to ground:
No Start from a shorted MAP sensor (Honda, Acura)

Yes, it's for Honda, but I believe the principle is the same. It's good to know that these circuits have protections in them (designed for sensors to fail) to avoid damage to the computer.

 

[edmaz]

Updates on my testing:

• All 3 sensors unplugged - Able to start engine
• Fuel rail sensor plugged in only - Able to start, a little rough at first
• Fuel rail + Manifold pressure sensor (MAP) - Cranks, no start

It sounds like you're saying the vehicle starts and stays running with the crank sensor disconnected. If so, I don't understand why that's happening, because the FSM lists a fail-safe for P0335 of fuel injection and ignition being stopped. I suppose it's possible that the manual could be wrong about that, but I'm wondering if you're actually working with the CKP sensor or not.

 

[AVC]

So the MAP and fuel pressure sensors are plugged in. How may codes remaining?

And if you then plug in CKP sensor?

 

[Ven Zoah]

So the MAP and fuel pressure sensors are plugged in. How may codes remaining?

And if you then plug in CKP sensor?

With only the MAP unplugged, there are just 6 codes. With the MAP plugged in, there are 12-27 codes.

It sounds like you're saying the vehicle starts and stays running with the crank sensor disconnected. If so, I don't understand why that's happening, because the FSM lists a fail-safe for P0335 of fuel injection and ignition being stopped. I suppose it's possible that the manual could be wrong about that, but I'm wondering if you're actually working with the CKP sensor or not.

Yeah, it is weird, but I believe there are two crankshaft position sensors (the other is in the back behind the water pump) and the one that is unplugged is crankshaft position sensor A (in the front near the HPFP and fuel purge valve.

 

[AVC]

There is only one CKP, passenger side, just behind the lower wheel well splash cover, low on the block.

There are TWO CMP's; one for intake on the radiator side of the valve cover, and an exhaust, on the cabin side of the valve cover, near the high pressure pump.

 

[AVC]

The point of unplugging the three sensors and plugging them in ONE AT TIME, is to see which sensor causes all those other codes (i.e. which sensor is killing the 5v or 12v reference).

If you believe the MAP is doing the deed, then plug in the MAP, turn the ignition on (two presses), but don't start it. Back probe the MAP sensor--use a t-pin or straight pin-- and measure voltages.

Put black test lead on - battery terminal and + test lead on each of the MAP sensor wires and note measurements.

Then unplug the MAP, leave the ignition on, and measure voltages at the connector. You can front probe the connector but don't push the meter probe into the connector sockets as it will deform them.

Don't use multiple pins as you don't want to inadvertently short adjacent pins.

Compare plugged/unplugged measurements.

You can do the same measurement scheme with the CKP. Or any other sensor for that matter.

 

[Ven Zoah]

There is only one CKP, passenger side, just behind the lower wheel well splash cover, low on the block.

There are TWO CMP's; one for intake on the radiator side of the valve cover, and an exhaust, on the cabin side of the valve cover, near the high pressure pump.

Oh okay, the one I'm talking about is here

 

[AVC]

That's the intake cam sensor.

The error you posted was for crank sensor (CKP).

This video shows where CKP is at: Crankshaft Position Sensor location on a (2014-2018) Mazda 3

 

[Ven Zoah]

That's the intake cam sensor.

The error you posted was for crank sensor (CKP).

This video shows where CKP is at: Crankshaft Position Sensor location on a (2014-2018) Mazda 3

Wouldn't failure of that sensor cause the engine to have no spark and just dump fuel? And would I not be getting an RPM reading?

I was able to start the engine with it plugged in and the tach was working fine. Are you saying that the P0335 code isn't for the sensor in this circuit here? Because that would make sense since the 3 permanent codes are the sensors here in this diagram.

 

[AVC]

I'm going off the codes you originally posted:

The codes are:

• P0069 - Manifold Absolute Pressure - Barometric Pressure Correlation
• P0335 - Crankshaft Position Sensor A Circuit
• P0193 - Fuel Rail Pressure Sensor A Circuit High

We'll go in circles unless you follow directions exactly, so we can get a clear picture of what sensor and related wiring is causing this.

So, now that we've cleared up where CKP is, lets go back to the beginning.

If you plug the MAP and fuel rail sensors back in (assume you've never unplugged CKP anywhere in this thread), and attempt to start the car, do you get the same list of codes as in post #19?

If you JUST unplug the MAP and attempt to start, what codes are there--post them, please!

If you plug the MAP back in and JUST unplug the Fuel Rail sensor and attempt to start, what codes are there--post them, please!

 

[Ven Zoah]

Update: I replaced the MAP sensor and it runs perfectly now! No codes!

I tested each sensor with my multimeter and found that the MAP sensor itself was indeed shorting the 5v reference loop. I went to Mazda earlier today and got a new sensor. Car runs and idles so smooth, it’s like new again. The carbon cleaning was def worth it. Thanks everyone for your help.

 

[yrwei52]

Update: I replaced the MAP sensor and it runs perfectly now! No codes!

I tested each sensor with my multimeter and found that the MAP sensor itself was indeed shorting the 5v reference loop. I went to Mazda earlier today and got a new sensor. Car runs and idles so smooth, it’s like new again. The carbon cleaning was def worth it. Thanks everyone for your help.

Thanks for the update.

And carbon cleaning should have nothing to do with the failed MAP sensor although the timing is very strange. I wonder what the Mazda dealer would do after they replaced the whole wiring harness and found the problem is still persistent?

What Is the part number and how much does it cost for the MAP sensor?

AVC and edmaz definitely are the big contributors helping you to resolve this rare issue. And I’d also say you yourself also is a contributed who did a hard work trying to resolve the issue and kept us posted.