I seem to have missing or mis-connected vacuum lines and trying to trace things down. One of them being the air pump (also getting error codes P0443 and P0414 which I think is related to it).

I found this diagram which isn't exact but good enough:


I am wondering where 19 should go to. I had this hose completely missing. Does this connect to the throttle body?

 

Sort of. 19 connects to the vacuum tree on the intake, below TB.

Here is why.

# 15a/b is the Secondary Air System (SAS) Solenoid. Solenoid is controlled by ECU, and its function in life is to let-thru or stop vacuum to the SAS Valve (# 8). Valve's mission in life is to allow Air (Pulsed Air) from the Air Pump (# 1) to be pulse-pumped onto the Exhaust Manifold.

P0414 means that Vacuum Solenoid for Secondary Air System (SAS) is not operable. Of course, there is no vacuum for it.

P0443 means "EVAP valve signal missing, Permanent Fault". EVAP Valve is in close proximity of SAS Solenoid, and maybe connector is loose?

 

Thanks, that's what I meant by TB. I connected it to there but still getting both same errors. I even got a spare SAS solenoid and EVAP purge valve but still getting the same two errors.

I should probably check the wiring now. I assume (easy to check when I get home) the plugs are different? As in, the two plugs wouldn't have been swapped across or anything...that would be terrible design if the two had the exact same plugs!

 

Wires Blue + Black go to SAS Solenoid.
Blue + Green/White go to EVAP Valve.

 

Well plugs are correct and replacing them with another set just resulted in P0444 and P0414. Im thinking the wires must be shorted somewhere? No short on the sensors at least when checked

 

In case you don't have them, Wiring Diagrams here

 

Thanks Henry, you've been amazing help so far. SO looking at the diagram, it makes sense that I also tend to get o2 sensor (both primary and secondary) errors because they all share the same hot line. Now I have to figure out where it's getting shorted.

As far as power to the two sensors (SAS and EVAP), the blue wire for both are around 11.5-6v so I would assume that is fine. I also did a continuity test between the blue to the chassi and does not seem to be shorting out.

What's odd is at one point when key is to ignition on, I got full continuity from the black wire on the SAS, and partial continuity on blue to the chassi. But this continuity was gone later on from both blue and black...so that must mean the connection is toggled by ECU somewhere?

Any idea where to start from?

 

First, I would check that Fuse 3 (5 amps) in Engine Compartment Fuse box is healthy. Secondly, I would check Fuel Injection Relay, just follow the Wiring Diagram. Unless there was a reason to, the ECU wiring harness is not easily shorted out.

SAS and EVAP systems are activated by ECU at certain conditions (like temperature, throttle position, etc) for certain duration (90 seconds for SAS, e.g.). They are on only for specific intervals.

Yet, their positive wire (blue), should always have 12V with Engine Running. ECU controls these devices by grounding them -- you know this already.

You can read more on Bosch Motronic 4.4 Logic here

 

Thanks, that would be exactly what I am seeing, where I have constant power to blue when ignition is on. I did already check the fuse and it is good and tried checking out the relay but other than externally looking I wasn't sure what you do to test relays.

I was thinking it probably wouldn't be the fuel relay though being that other than the error codes, the car seems to run fine. I imagine if the fuel relay was going out, you would notice quite a bit of hesitation when driving?

Being that you mention the ecu main harness rarely shorting out (I assume because of how much protective wrapping these usually have?), I am thinking of tracing the o2 wiring since that tends to be close to a lot of hot surfaces such as exhaust...I already changed out the primary so that wiring is good, but I did notice how some of the wiring was not secured well...maybe a good thing to trace those wires on the secondary as well.

Other than that, any other suggestions on wiring to check? I assume just tracing the wire from both EVAP and SAS (blue wire) from sensor to fuse box?

 

Last thing I would check before I dig into the harness is the ground points. I would clean them and apply dielectric grease. They are listed on the "Ground Distribution Circuit" page in the 1-Line Wiring Diagram I posted.

You can check relays for voltage. Signal wire (from the ECU) should be generally 5-6 volts.

 

Thanks Henry, I haven't been home since then but will check those. I have been thinking about the wiring diagram in my head and have a theory:

Being that I see continuity on the blue wires ONLY when the ECU connects the ground for these two sensors, I would think it has to point to a bad sensor. If any of the blue wire was shorting out, it would show continuity between the wire and chassi regardless of whether ground was connected or not, yes?

So being that's the case, the only other sensor that hasn't been changed is my secondary o2 (I swapped out the EVAP and SAS, installed a new o2 primary).

Like I said I will check ground points and also the relay voltage...but based on what I stated above, I'm thinking it indicates that a sensor itself is probably shorting. Let me know your thoughts...

 

It depends, often wire shorts / loose grounds show their true colors under vibration.


IMO your symptoms are classic examples of wiring / ground faults, not a particular sensor (including rear O2).

Swapping parts, before diagnosing, is usually a waste of time and money. I know have wasted plenty myself.

 

I completely agree. I just happened to have already ordered the secondary last week so we'll see what happens. For the grounding, do you recommend checking all those grounding points? Some sound hard to find...below front seat?? Either way I will if you think that will pinpoint it.

For the secondary o2 sensor, I just unplugged and turned on car after resetting the light..oddly enough it stayed off for a few min and then engine light came on again, with the same P0444 and P0414. So I guess it still indicates a short...but I am surprised I didn't get a code for the secondary o2 sensor.

 

Just the 3 or 4 grounds in and around Engine Compartment. Go by the Wiring Diagram, because you may not eyeball everything around there.

BTW: both SAS Solenoid and EVAP Valve are easy to check. Apply 12V (correctly) and you should be able to blow thru. They are really simple devices.

As you know, rear 02 sensor is there to measure Cat efficiency, and it is not vital in engine management. So maybe its DTC (P0422) is "pending". It may need several drive cycles to store a permanent P0422 and light up the CEL. Can your OBD Scanner retrieve pending codes?

Your original post indicated P0443 (EVAP signal missing, permanent fault), now you report P0444 (Signal too high. intermittent fault). DTCs being all over the place -- that seems like a loose ground or loose wire, under vibration.

On SAS: does your Air pump work when you apply 12V to it?

 

Thanks, I will check all the grounds in engine compartment based on the diagram.

For my reader, it does read pending codes but so far nothing has shown but again, I haven't really driven it...so you may be right, that it will take a few cycles before the o2 sensor code pops up. And yes, it's odd that the code switched from P0443 to P0444. I think you may be on to something with that as well since even the o2 sensor codes switched between a few of the P013x range over time. Checking grounds will def be my next step...based on the loose items I have already found, I wouldn't be surprised if I find a loose or disconnected ground.

For testing the pump and sensors, can you advise on the proper way to apply 12v and test it? I assume getting a ground on chassi and another off the battery or something is not advised?

 

I connect them to battery posts, with correct polarity of course. Now that you have the wiring diagrams, you know which ones are + and -.

 

Got it. So you recommend ground on battery rather than chassi? I thought I remember reading that the chassi is better ground than the battery. But either way, it sounds like I have the right info to test these out.

For air pump - I should hear the blower turn on?
For SAS and EVAP, I should be able to blow through once turned on?

For checking voltage on relay, do you just pull out the relay and check voltage in the pin holes?

 

Yes


Yes


The right way is to leave the relay connected, needle-clip on the wires/terminals and measure voltage. Of course, basic knowledge of relay operation, wiring diagram, and ECU logic is necessary to know.

Again, I would check the grounds first. Many people here have complained about bad grounds. Have you cleaned them yet?

 

I was just trying to check the grounds right now and spent a few hours but very unsuccessful. I can't find the grounds that it says should be there...which maybe the problem?

I started to trace the short to see if I can isolate around where the short would be. I eventually got to the battery positive terminal...I get continuity from the positive terminal to the chassi! No good.

I need to try and find a diagram of the grounds rather than a description because I think the ones that should be there are missing. arg...

 

For example, there is a ground under the air pump. Another one on the firewall passenger side. They are ground straps/wires bolted to chassis steel.