JJ291

When I rebuilt my engine I guess I was tired during the installation. I ran it for a minute or so and the CEL came on. I check the code and it was P0135/P0141 O2 sensors. I checked them out and like a serious moron I had somehow plugged the ECM/PCM connections into one another and the O2 sensors into one another...yes, I know. I thought no big deal, plugged them in the right spot but no luck - CEL stays on now.

I've been through the whole diagnostic and keep ending up at the same spot - replace the ECM/PCM with good unit and see if problem goes away. I replaced both sensors which did nothing and now about to replace ECM/PCM but just want to get a gut check on if I fried the computer?

Thanks.

BTW - life gets aggravating when you do stupid things.

xRiCeBoYx

iTrader: (22)

First time I did a HG change, I forgot to plug in a sensor. Car ran like **** and threw a CEL. Plugged it back in, reset the code, all was well.

Often times, unless you reset the code(s), the light will remain on. You probably didn't have to replace the sensors, to be honest, just reset the code after plugging the sensors in and call it a day.

JJ291

Honestly, you won't hurt my feelings a bit if you call me a total moron. I've unplugged the ECM fuse, erased the CEL, ran through the service manual diagnostic, blah blah. What else can I reset and how do I do it?

xRiCeBoYx

iTrader: (22)

Did not know you did all that. CEL still on after all that, I'm assuming?

edit: I'm also not one to call you a total moron for simple mistake like that. Calling people moronic is reserved for those that are scared of stupid things, like "it's cold outside, and my heater takes too long to warm up. I think i broke my car. Help" or "I washed my car and a little bit of water got into the engine bay. I think my car's going to hydrolock if I start it." I can think of a few (not-so active) members that come to mind when I think about "moronic." lol

We've all had our dumb moments, it's how we handle them is what matters. You're owning up to it and asking for legitimate help after doing some DIY diagnosing.

That said, if you could give us a rundown of anything relevant you did post-rebuild (basically anything you did after the codes popped), that'd help a bit. On top of pulling the ECM fuse, just up and disconnect your negative battery terminal for a good 10 minutes. While that's going on, double check all the sensor connections, any sensor you may have touched during the rebuild. Make sure everything is copacetic, reconnect battery, and try again.

JJ291

Yep. Replaced both sensors. Reset the ECM/PCM. Erased the code with OBD. Went through diagnostic for primary and secondary - have battery voltage at the heater and no shorts anywhere as far as I can tell. Checked A1, A14, A25 on the ECM and no continuity.

No idea why it's not picking up other than ECM not accepting it.

....aaaahhhhh!!!

ezone

What testing did that entail?
More like, what testing did you actually do? What were the results?


Disconnect the battery cables and short them together for 10 minutes instead.




Pick a sensor heater circuit (code trouble shart*) and check upon starting the engine: Got power? Got ground?

Blown fuse(s) for the O2 heaters?




*not a typo. Trouble trees mostly get you into a bunch of trouble (shart).

ezone

What do your sensor heaters ohm at?
Did you get OE sensors NTK or DENSO, or did you get brand x?

JJ291

Here goes:

1. When I pulled the engine I forgot to unclip the secondary sensor and ripped the wires out of the electrical connector
2. I reconnected them into the connector but I did not take the time to see if I did it right and gambled like a dumba$$ because they were still "grouped" together
3. (BTW - did I mention that I started celebration beers early)
4. Then, in an effort to outdue my first mistake, I accidentally connected the sensors together and the sensor ports to one another
5. I started the car and got the CEL - found the sensors and corrected them. CEL stayed on.
6. I went through the P0135 and P0141 diagnostic in the service manual
7. I ohmed the old sensors and the secondary had ~15 ohms and the primary had about 4 ohms
8. I checked for battery voltage across the 3/4 wire and had 12 volts
9. I disconnected the ECM/PCM A31 and verified I did not have a short at the A1 and A14 points (I'm doing this from memory so #'s may be off)
10. Then I replaced both sensors - I was able to get a Denso for the secondary but had to get a Bosch for the primary (original was NTK)
11. I went through the whole process again
12. Ohms were similar to before
13. I also disconnected the no. 10 fuse and reset the ECM/PCM - still on
14. I checked the no. 4 ACG 10 amp fuse and it is not blown

I studied the electrical and circuit diagrams. One thing I found funny was that I connected an alligator clip from the ground side of the connector (no 3) to my multimeter and to the A1 connector to try and form a loop and checked for continuity and did not get it. however, it feeds through the alternator circuit so this may be a bad assumption on my part.

I will disconnect the battery as recommended and let you know how I go here in a bit. Thanks!

JJ291

OK - tried disconnecting the battery leads and shorting them together for 15 minutes. Also reset ECU but it came on right after starting.

Since it sends battery voltage to the heaters and i was essentially running them straight to ground, I'm wondering if I overheated the output element in the ECM/PCM and just fried it.

ezone

Just how early did you start celebrating??? LOL



I have having to search for car info.
Engine harness connector, or sensor connector?

Um, did you triple check your wire positions in each connector? They are not identical to each other ----even though 3 wire colors are the same, they do not occupy the same positions in each connector..
Compare to another 01-03 LX car if necessary.

Hell, make sure the wires below match up to the pair of identical colored wires on each sensor (typically 2 blacks or 2 whites for the heater)

-----------------------------------

Ok fuse 4 feeds + to the heaters on both sensors on the black/yellow wire.

Ground is controlled by the PCM on A1 and A14, both black/white.



A voltmeter cannot load a circuit.
You need a load now.
Get a #194 bulb to use as a test light. Straighten out the wires so you can stick it in a connector.



Plug the test light into the primary connector (engine harness side) and see if the PCM can supply enough current to light up a #194 bulb when you start the engine.

It may flash, it may go out (due to incorrect current draw, it can't match the actual heater) but the PCM should be able to supply enough current through the output driver to make it light.

Do the same for the secondary sensor connector. The PCM may not turn the heater on right away, it may take a minute.


What about the NEW sensors?
Are the old sensors still usable?


Manual says 3.0-3.6 ohms for the primary sensor heater resistance and 10-40 ohm for the secondary.

I'll have to check my notes on the laptop at work for actual sensor resistances. The PCM is picky about this.


Another thing to think about: Stuffing things (probes) into the female wire terminals can spread them out so they don't make good contact with the male terminal anymore.

JJ291

Apparently much too early, lol.

Great idea - will need the weekend to get this one done. Thanks for the suggestion...great idea! Who'd have ever thought of that except ezone!

JJ291

Getting the 194 light bulb today. However, last two days the cat converter has gotten ... smelly. Like my cars been eating eggs.

Not sure if this is a cause or symptom but thought I'd throw out the additional clue.

ezone

Not right, I'd guess it's running unusually rich. I'd want to be reading what the O2 sensors are doing (if they are still connected).

Maybe unplug both O2 sensors (and do a battery reset to erase stored fuel trim values if possible) and see if the smell dies down.

JJ291

Tried the #194 light bulb, reset the ECM, connected the light bulb to the #3/#4 wire on the primary sensor and the secondary sensor and no dice. Waited about 2 minutes.

I also put an AC ammeter across the #4 wire and it would not measure anything.

Last thing I know to try is to jump all four connector points to the sensor and put my multimeter inline and try to measure amps.

I'm thinking there aren't any at this point since the #194 should only require 3.8W/14V = .27amps

ezone

You are testing in the engine harness connectors, correct? Not the sensors?

You said you had positive at each of the sensor connectors, correct?
Now-- if all else is correct -- this shows you must have no grounding from the PCM.
Fried.....?

Pointless if it can't even light up the bulb.

Wait, AC ammeter? This is DC current here.

You're making this overcomplicated.
You should backprobe the heater circuits and look for power and ground instead of trying to use an ammeter.
Also, I think there's no ground as the bulb can't even light up.

If I were going to use an ammeter, I would just peel some of the tape back from the harness just far enough to wrap an inductive ammeter clamp around a single wire.

Still pointless if it can't even light the bulb.
No bulb means no load to measure.


Right.

Looks like you fried your PCM?

Pull it out, locate the A1 and A14 or whatever they were, and follow the traces around the board to find the 2 output drivers, see if they have little holes smoked in them?

JJ291

Hey I'm dumb but I'm not stupid, lol. Yes, harness connector.

I went back at it again and here's where it gets weird. Earlier, I only tried it between the #3/#4 connector on the primary and secondary (on the engine harness) and it did not light up. I went back and tried it between the #4 - light - ground and it did light up. So...no ground on the #3 to A1 or A14 right? But how come I'm measuring 12v across #3/#4 with my multimeter? Maybe I'm missing something but if I've got 12v across them then I'm grounded right?

I checked the SM just to make sure I'm not losing my mind and the first thing they have you check is for voltage across #3/#4. If it is there they have you look for a short between the #3 and the A1 or A14 which would make sense. However, it's not there they have you check for 12v from #4 to ground and if you have it then look for a broken wire between the #4 fuse and the harness connector...

Hey at least the light lit up!!

ezone

You keep referring to 3 and 4, but you really need to go by wire COLORS.
I still don't know which connectors had the wires yanked out or if they got placed in the correct positions upon reassembly.
Always triple check wire COLORS!

The heater portion of the sensor needs power and ground to operate, and the sensing portion of the sensor also has its own ground circuit that is not the same as the heater ground.

2 wires for the heater.
2 wires for the sensor.
4 wires total. None can be interchanged!

JJ291

Sorry, I'm not communicating very well. When I pulled the wires out they came out of the sensor side of the connection. So I replaced the sensor that was damaged. During the course of troubleshooting, I replaced the other sensor as well.

So I have two totally brand new sensors albeit they are not OEM which I believe were NTK. I verified that the #3 and #4 connection in the diagram in the service manual matches up by checking the resistance on the sensor side of the connection and it does match the specified ohms.

I never pulled any wires out of the engine harness side of the connectors so - I think - I don't have any wires interchanged. Harness side is OEM, sensor side is brand new.

ezone

Oh yeah...
The multimeter does not load the circuit.
The output driver might only be able to supply 0.0001 amps.... and the meter would be able to read it..... But as soon as a load (test bulb 0.27 amp) is placed on the driver it goes open circuit.

ezone

Ok gotcha.

ezone

Black/yellow and black/white wires at each sensor connector. Bulb should light.


Wire positions 3 and 4 are not the same circuit on each sensor.
#4 on primary sensor is grounded by the computer.
#4 on secondary sensor is power from fuse.
Basically the power and grounds are flipped.
Make sense?
Checking colors should make this more clear!

The multimeter does not load the circuit.
The output driver might only be able to supply 0.0001 amps.... and the meter would be able to read it..... But as soon as a load (test bulb 0.27 amp) is placed on the driver it goes open circuit.

JJ291

Focused just on the primary last night and only on wire colors after reviewing the schematics. Put a 10 ohm resistor on the circuit but not to to the ECM ground circuit but rather grounded on frame.

Resistor got hotter than hades and the light bulb lit up. Tried it through my multimeter to measure amps again and nothing. I finally thought I'm going to try one more thing - got my $5 harbor freight multimeter out just to see if my nice one was wrong...how can the resistor get hot with NO current!

Sure enough - my multimeter is dorked up and I was getting 1.06 amps.

So - it's got to be in the ground circuit. Going to focus on just the primary today and pull the ECM as you suggested. Crazy.

JJ291

I don't know - getting pissed off at this thing.

Focused on just the primary today trying to get rid of the P0135 code and isolate the problem.
- Reset the ECM every time I started a new test.
- Inspected ECM/PCM - no visible signs of any damage on either side of breadboard
- Measured for continuity from the blk/wht at the primary harness (not sensor side) side back to the A1 pin and had continuity so should have no open wires!
- With the ECM/PCM opened up and all harnesses connected (including sensor) tried to go straight to ground at A1 pin by connecting clip from A1 pin in ECM to body ground
- With everything connected as it should be (including the O2 sensor), verified battery voltage across sensor connector and measured ohms across sensor. Started at 6 with no voltage, went to about 40 with battery voltage, and about 60 with car started.

For both primary and secondary:
- Connected a 10 ohm 10W resistor into the blk/yel sensor harness.
- Measured 1.05 amps across each resistor when I went straight to ground.
- Measured 16 and 18 milliamps on the primary and secondary, respectively, when I went back to the BLK/WHT wire (ECM ground).

Tried everything with the old sensor NTK and new sensor Bosch.

Seems like the wiring circuit on both primary and secondary is good all the way back to the ECM. Maybe I did some internal damage to the ECM in a microchip and will need to replace it. Just hate to go to all that effort and find out it isn't fixed.

The only thing I couldn't understand from the diagrams that was part of the diagnostic is why I would need to have battery voltage from A1 to A5. However, I checked it and verified that battery voltage was present.

All out of ideas - any last bets?

ezone

At work in the shop, I probably would have pulled the trigger on the PCM many posts ago, as soon as I figured out the PCM had lost the ability to supply ground to the sensors, yet all else was ok.

Studying the wire diagram, it would seem that if you connected the two sensor connectors together you would have connected power directly to both of the heater circuit drivers. As soon as each output driver was activated they got 'fried'.


Any replacement PCM will need to have the immobilizer programmed before the engine can run. They will need all your keys present.

JJ291

Well. Tough lesson to learn but it's not the end of the world - just want to get them corrected before I screw up my CC.

Ezone - I really appreciate your help. Only some people will help a stranger. Very few will help a nameless faceless virtual person. It's guys like you that make this forum.

JJ291

New ECM on Ebay - $80
Reflash at the Stealership - $140

.......

Having the Check Engine Light off....priceless.

ezone