Emissions or ECM problem

Today my 2014 Tacoma V6 started running rough with a pronounced stumble around 40 MPH. Brought it home, limping badly, and read OBD2 code P0306 Cylinder 6 Misfire. I swapped the coil from 5 to 6 and 6 to 5, and took a look at the number 6 sparkplug, which was fine except it smelled of gas.

When I read the OBD2 codes again, expecting a new code on cylinder 5 and 6 to be ok, instead I received a cascade of codes.

Here is a better list of codes just read:

OBD-IIOBD-II
DTCs: 6
----------------------------
P0300 [0x0300]
Random/multiple cylinder(s) - misfire detected
Random/Multiple Misfire Detected
Status: Confirmed
----------------------------
P0303 [0x0303]
Cylinder 3 - misfire detected
Cylinder 3 Misfire Detected
Status: Confirmed
----------------------------
P0304 [0x0304]
Cylinder 4 - misfire detected
Cylinder 4 Misfire Detected
Status: Confirmed
----------------------------
P219B [0x219B]
Mixture control, bank 2 - value out of range
Status: Confirmed
----------------------------
P0306 [0x0306] Archive (inactive)
Cylinder 6 - misfire detected
Cylinder 6 Misfire Detected
Status: Permanent
----------------------------
P1604 [0x1604]
Code Word Unregestered
Status: Confirmed
============================
Engine control unit #1Engine control unit #1
DTCs: 5
----------------------------
P0300 [0x0300]
Random/multiple cylinder(s) - misfire detected
Random/Multiple Misfire Detected
Status: Confirmed
----------------------------
P0303 [0x0303]
Cylinder 3 - misfire detected
Cylinder 3 Misfire Detected
Status: Confirmed
----------------------------
P0304 [0x0304]
Cylinder 4 - misfire detected
Cylinder 4 Misfire Detected
Status: Confirmed
----------------------------
P1604 [0x1604]
Code Word Unregestered
Status: Confirmed
----------------------------
P219B [0x219B]
Mixture control, bank 2 - value out of range
Status: Confirmed
============================
ABS control unit #2ABS control unit #2
DTCs: 2
----------------------------
U0073 [0xC073]
Control module - data bus Off
Status: Confirmed
----------------------------
U0126 [0xC126]
Data bus, steering position sensor control module - no communication
Status: Confirmed
============================
Dashboard/Instrument cluster #1
No DTC found.

Thanks,

Bob

 

Always start with U codes first even though it may seem unrelated. I'm not a Toyota Mechanic and a guy like @Bishop84 can be specifically more helpful than I. However it's likely the steering angle sensor is on the same network as the ecm (high speed CAN) so it's possible that a glitch in it could be messing with the ECM.

Otherwise, a compression test among the other basics would be what I would check after sorting out the network issue.

Side note: it's a good idea to also switch the spark plug to a separate cylinder than where you switch the coil as the plug can also fail internally

 

I usually ignore U codes to start, but this is a pretty odd issue.

I'd be looking mechanically first, I'd be suspecting a leaking injector possibly, but usually you'd have a flashing engine light with this.

It's a lot to process and imbalance codes are rough to diagnose.

 

**shyly backs into a dark corner**

 

I say usually but this may be related, most U codes show up as history codes to us.

 

Sure you swapped 5 & 6?

I would usually swap the coil/plug right next to each other not across the motor.

Could be why the new codes causing more confusion.

 

You're right Dillusion, I swapped 4 and 6.

 

I wouldn't worry about the U codes or AFR imbalance just yet, a weak battery can cause U codes to set.

The AFR code is more likely an effect than a cause.

Will your scanner show live data so you can see which cylinder(s) are currently misfiring? Sometimes a single cylinder misfire can set codes for multiple cylinders if it is misfiring badly enough.

 

I don't think my OBD reader app shows live data, so I cleared all the codes, then restarting the engine, I took another look.
One code appeared:
Cylinder 4 Misfire.

Thanks for the advice on a recheck of codes. Headed to Auto Zone right now. I'll let you know.

 

I changed the number 4 coil pack and it's back to running well. As a backyard mechanic, (I'll break anything at least once), it's perplexing to me how a bad coil pack causes the ECM to throw so many codes. Sickly dread was washing over me.

Thank all of you very much!

By the way, Car Scanner ELM OBD2 seems like a good Android app.

 

Like I said when a misfire is severe the PCM can't always tell which cylinder it's on and may flag misfires on multiple cylinders, also with a misfire your gona have a skewed AFR sensor reading because no or incomplete combustion is taking place in a cylinder.

 

Intertesting, in chevy land, Every module will throw codes and you end up with minimum 7 codes for a issue.

Usually they're just saying they're getting invalid data from the module reporting the actual code but i've been burnt by disregarding them fully before. Had a cylinder 2 misfire caused by a lost in communication to the rear diff module that I caught my ass on

 

That's pretty much the case for any modern vehicle, systems are so interconnected now that a fault in one module causes every other module to set faults.
Usually by the time they get to me either the codes have been cleared and I have to scratch my head or they have so many codes in them I just document them, clear them all, and see what comes back.

That's interesting, never seen that before.
I see so many U codes even in perfectly functioning vehicles that I don't typically pay much attention to them unless they are persistent and related to the problem I'm trying to address.
Half the vehicle's I see have shit batteries in them so U codes and low battery voltage codes are pretty normal to see.

 

That was my thought process at the time too and I still think it's a good system... that just happened to be my introduction to networking when I was an apprentice so it's forever tainted me aha

 

Hi @joba27n 1101 0110 0111 1010 0010 1110 1100 1111

 

...hello...