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Recurring error code P0748 (Solenoid Valve A)

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wwdwgs

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Discussion starter · #1 ·
I had this code before and traced it to bad wiring. I ran new wires from this valve to PCM. Soldered. The problem was gone...
After a couple of hundred miles the same code popped up.
Observation:
After I fixed for the first time, I noticed some strange behavior - one of the red lights on an instrumental panel will flash for a split second (while driving) - just barely noticeable. I thought that it was just a sun hitting an instrumental panel.. But.. today, just before this P0748 code came up, "doors open" warning lights illuminated for a split second. Then, D started to flash and CEL/TCS were on.
Off course, acceleration in D was very slow, and I had to manually shift from 1, to 2, to D3.
Thought:
What I didn't check (visually) were the crimped connections between wires and pins in all affected plugs. Knowing that wise Honda engineers crimped copper wires in aluminum connectors, I could suspect that copper oxidized inside the crimp.
So, in order to inspect them, I have to dismantle each plug and remove affected pins.
As I understand, in order to remove a pin from a plug, I have to insert a thin piece of metal in a slot (facing a plug) "above" pin connector and pull out the wire (together with a pin).
I tried to remove one from PCM C connector before, but the pin didn't even think to move.
Questions:
what prompted quick flashing of lights on an instrumental penal before?
what is the correct way to remove pins from a plug?
2002 EX with 253000 miles.
 
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Discussion starter · #2 ·
update:
I checked connectors of Solenoid Valve A - they are clean.
Tried to pull out wires from PCM B connector (corresponsing red, white (pins 1 and 8?)), but couldn't do that. Either white lock tab was still holding them, or pin wasn't big/flat/long enough to disengage the pins.
Nevertheless, when I assembled everything back, started the car, ran it for a few minutes - no codes...
In all this excitement , I drove the car today, to extinguish flashing monitors. When they extinguished (after about 7-8 miles), I rolled to a traffic light, put into neutral, then to D and ..... D started to flash again - error code P0748 came back.
I understand, that one needs some excitement in one's life, but not so frequently!!!!
Swap PCM for an original one? I don't know what else can be done...well, I can get my favorite drink...
 
Discussion starter · #3 ·
yet another update:
Original PCM is indeed faulty - it shows Prim O2 sensor's voltage at constant 12.x Volt. It was replaced with a used unit, which shows normal up-and-downs in Prim O2 sensor V. P0748 was deleted. Drove 1/2 mile and P0748 came back (with blinking D, of course).
That's strange - solenoid by itself is good (impedance is within normal range), it does move when voltage is applied and wiring is good too (tested with test light) - I activated this solenoid by injecting 12V from PCM side (again - with test light) - kicks like a mule.
Currently, error codes are deleted. but, somehow, I feel that this error code may come back, if I'll drive tomorrow.
Question - if I'll decide to replace Solenoid Valve A (part # 28250-P6H-024 ) with a new unit, which aftermarket brand(s) is(are) good?
 
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#4 · (Edited)
wwdwgs said:
yet another update:
Original PCM is indeed faulty - it shows Prim O2 sensor's voltage at constant 12.x Volt. It was replaced with a used unit, which shows normal up-and-downs in Prim O2 sensor V. P0748 was deleted. Drove 1/2 mile and P0748 came back (with blinking D, of course).
That's strange - solenoid by itself is good (impedance is within normal range), it does move when voltage is applied and wiring is good too (tested with test light) - I activated this solenoid by injecting 12V from PCM side (again - with test light) - kicks like a mule.
Currently, error codes are deleted. but, somehow, I feel that this error code may come back, if I'll drive tomorrow.
Question - if I'll decide to replace Solenoid Valve A (part # 28250-P6H-024 ) with a new unit, which aftermarket brand(s) is(are) good?
Click to expand...
unplug both connector pcm and solenoid do short to ground and short to power test each wire. if you find some reading in either one wire overlay that wire and (cut run another wire) road test see what happen.... or run a new wire to test if there is some issue when at the time of test driving suddenly become short to ground or short to power, this is just verify your wiring integrity.
 
#5 ·
jdm06ody said:
unplug both connector pcm and solenoid do short to ground and short to power test each wire. if you find some reading in either one wire overlay that wire and (cut run another wire) road test see what happen.... or run a new wire to test if there is some issue when at the time of test driving suddenly become short to ground or short to power, this is just verify your wiring integrity.
Click to expand...
 
Discussion starter · #7 ·
update.
The wires running from solenoid to PCM B pins are new....
I just re-tested them with test light - they pass current well. BUT...
I noticed something strange, in my opinion. When I actuated solenoid with test light from PCM side (injecting 12v to red and white wires), solenoid "clicked". If I repeat actuation right away, solenoid doesn't click. if I wait 2-3 seconds (or more), activation works and solenoid clicks. Light in any instance is lit.
is solenoid sticking? or is it burnt (windings)?
When I tested it before (a couple of weeks ago), I applied voltage directly to solenoid's pins and it worked (clicked) any time I touch it, even 10 times a second. Now there's a delay between "clicks".
Time to check solenoid's resistance again....
 
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#8 ·
wwdwgs said:
update.
The wires running from solenoid to PCM B pins are new....
I just re-tested them with test light - they pass current well. BUT...
I noticed something strange, in my opinion. When I actuated solenoid with test light from PCM side (injecting 12v to red and white wires), solenoid "clicked". If I repeat actuation right away, solenoid doesn't click. if I wait 2-3 seconds (or more), activation works and solenoid clicks. Light in any instance is lit.
is solenoid sticking? or is it burnt (windings)?
When I tested it before (a couple of weeks ago), I applied voltage directly to solenoid's pins and it worked (clicked) any time I touch it, even 10 times a second. Now there's a delay between "clicks".
Time to check solenoid's resistance again....
Click to expand...
if you suspect solenoid is going bad get another used good one or new one put it on to verify. hopefully will fix the problem
 
Discussion starter · #9 ·
Solenoid's resistance is within specs - 6.5 Ohm.
I'll give it another try and clean it thoroughly, dry it, lube and see how it will behave...
 
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Discussion starter · #11 ·
This solenoid is removed and was tested. Looks like it moves "ok" first time, and, then doesn't move well (very short travel of pintle). After "recuperating" for a few seconds, it does the same thing.
Here's how it looks like: https://cloud.degoo.com/share/20LiN-qzQFNCv8sus0Bfww
 
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#13 · (Edited)
wwdwgs said:
This solenoid is removed and was tested. Looks like it moves "ok" first time, and, then doesn't move well (very short travel of pintle). After "recuperating" for a few seconds, it does the same thing.
Here's how it looks like: https://cloud.degoo.com/share/20LiN-qzQFNCv8sus0Bfww
Click to expand...
CHECK no 6 (15A) in the drivers under dash fuse/relay box make sure 12v is present on the solenoid harness pigtail.
 

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Discussion starter · #14 ·
jdm06ody said:
CHECK no 6 (15A)
Click to expand...
I check this fuse religiously in the morning, afternoon and evening. It's in my dreams, floating and bouncing around! It even talks to me!
Regarding checking a voltage at Solenoid Valve A: how do I do that? Is it constantly under the current? Do I hook up meter, turn on ignition to II and check?
Like I said before, I did activate this solenoid from two wires right by PCM (unplugged B connector and injected 12V, hopefully with correct "polarity").
Be the way, I just installed a used replacement Solenoid Valve A-B. I checked it before installation to make sure it moves completely every time and any time I close the circuit. It does. So, after installation I'm back to square one - D light blinks, computer gives me P0748 code. Even with deleting all codes..
Regarding 4-th gear solenoid: your sample above talks about other codes as well. I only have P0748.
So, at this point, I will install a second used Solenoid valve a-b and see what'll happen next. I kind of know, rather anticipate, a result. I would like to be wrong this time.
 
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Discussion starter · #15 ·
Update:
insanity! Wiring form solenoid valve A (pressure control solenoid valve A) to PCM is good, positive(red PCM B17 and negative white PCM B8). Tested from terminal pins with test light.
Codes erased and P0748 re-appear again.
WTF??!!
Other testings:
Valve itself was directly powered to 12V - works greats - click anytime I close the circuit.
When I test valve from PCM B plug, injecting the same 12V, valve work onlly for the first time and doesn't move if I repeatedly close circuit. The valve needs 2-5 seconds to start operating again; and again: first time - good, then no respond within a couple of seconds.
Is it high resistance of new wiring?
is ti high resistance somewhere inside PCM?
If it is indeed high resistance, then the test light will be dimmer, than usual.
I just don't understand.
BTW, I cut old wires close to the pins and the new wires are soldered to the remaining wires.
New wires are 18 or 16 ga.
 
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#16 · (Edited)
wwdwgs said:
Update:
insanity! Wiring form solenoid valve A (pressure control solenoid valve A) to PCM is good, positive(red PCM B17 and negative white PCM B8). Tested from terminal pins with test light.
Codes erased and P0748 re-appear again.
WTF??!!
Other testings:
Valve itself was directly powered to 12V - works greats - click anytime I close the circuit.
When I test valve from PCM B plug, injecting the same 12V, valve work onlly for the first time and doesn't move if I repeatedly close circuit. The valve needs 2-5 seconds to start operating again; and again: first time - good, then no respond within a couple of seconds.
Is it high resistance of new wiring?
is ti high resistance somewhere inside PCM?
If it is indeed high resistance, then the test light will be dimmer, than usual.
I just don't understand.
BTW, I cut old wires close to the pins and the new wires are soldered to the remaining wires.
New wires are 18 or 16 ga.
Click to expand...
MEASURE THE VOLTAGE BETWEEN PCM CONNECTOR TERMINAL D5 & B20 OR B22
IGNITON ON IF VOLTAGE IS PRESENT SUBSTITUTE WITH A GOOD KNOW PCM AND RECHECK. IF NO CHECK FUSE 6 15A DRIVER UNDERDASH OR PCM POOR GROUND (G101).
IF ALL TEST WERE GOOD THE FLOW CHART PIN-POINT TO TRANSMISSION IT SELF. YOU CANNOTGET AWAY IF MECHANICAL FAILURE YOU HAVE TO EITHER REBUILT OR REPLACE.
 

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Discussion starter · #17 · (Edited)
jdm06ody said:
MEASURE
Click to expand...
in order:
I cleaned 3 ground points in the engine bay: G101 (below starter), and two others where the ground wire connects to somewhere above starter and to the front frame just above alternator. The contact points were not oxidized at all - mating metal surfaces were "relatively" shiny. I still sanded them, greased and re-assembled.
From PCM side I did measure voltage between D5 and B20/B22 - it was 12.X V.
I didn't install other "known good PCM" as A) I didn't have one and B) didn't make sense to me, because, if there's no voltage at above PCM connector, then "check fuse #6". This would suggest that blown fuse (failure) won't pass voltage (also failure) and voltage must be present, when fuse is OK. Fuse was good. Why to change a PCM?
Next.
After confirming voltage, I plugged in a scan tool, cleared the codes, no codes - no blinking D, started the car, no codes -no blinking D, went through drive cycle to extinguish incomplete monitors. No codes - no blinking D.
Overall miles driven after this "fix" - about 50.
For now, current problem P0748 is resolved.
Thank you all, who participated and helped me.
 
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wwdwgs
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