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03 Ford Ranger 4.0L SOHC
ECU/EPM pin #28, it's one of the 4 wires to the MAF, Tan and light blue, but in the schismatic it gives me no indication as to what this wire is for, the other 3 are the signal from the MAF, voltage and ground. I have 2 CEL codes, one for the MAF and one for air temp sensor. I'm suspecting bad wiring since I had a bad wire to an injector I had to bypass to get it to fire and replacing the MAF didn't solve this problem so before I go spend an hour trying to check the continuity of the wiring, does anyone know what this tan/lt blu wire is? Is it for am internal air temp sensor in the MAF or something else?
I have tan/light blue wire as pin 36 for MAF sensor return
Then light blue/red to pin 88
The 2 MAF sensor wires
Red and black wires are for the MAF heater, 12v and ground respectively
Then IAT(ACT, air temp) use
Grey/red wire which is a shared wire with TPS, ECT, ISS, OSS and a few other sensors, 5volt, from pin 91
Grey wire goes to pin 39 signal wire
Pin 28 is transmission solenoid D, brown/orange wire
I looked at a few years and did not see 28 used for MAF
The PDF you supplied me a few weeks back, "2002 4.0l 4" shows pin 28 as TAN/LT BLU unless i'm mistaken, 34 as red (voltage), 103 as BLK (ground obviously) and then 88 as LT BLU/RED as MAF.
May I ask, what are these, I duno what to call them, junctions? S101 and S107? Also noted in the picture are 6 wires on that plug but the drawing on shows 4?
Good catch Supercab I never looked/thought of wire legends
The MAF sensor only has 4 wires, so diagram is correct
The IAT/ACT sensor has 2 wire, and should be part of the diagram but not with MAF sensor, since they have no connection
These are separate devices on the drawing, they were combined into one connector in the early 2000's but are still separate devices sharing a connector and housing
Those wires are at the "end of service life", hit a wrecking yard and get a new 6 wire connector WITH same wires attached, then cut and splice to your wires
And "S" on a drawing means splice, "C" means connector
S101 would be "splice 101" for that YEAR only
C101 would be "connector 101" for that YEAR only
Good catch Supercab I never looked/thought of wire legends
The MAF sensor only has 4 wires, so diagram is correct
The IAT/ACT sensor has 2 wire, and should be part of the diagram but not with MAF sensor, since they have no connection
These are separate devices on the drawing, they were combined into one connector in the early 2000's but are still separate devices sharing a connector and housing
Those wires are at the "end of service life", hit a wrecking yard and get a new 6 wire connector WITH same wires attached, then cut and splice to your wires
And "S" on a drawing means splice, "C" means connector
S101 would be "splice 101" for that YEAR only
C101 would be "connector 101" for that YEAR only
This morning I did check continuity of the wiring from the plug to about an inch back into the wiring just to make sure the plug was the problem before bothering to order another. Yes it needs replaced, but doesn't appear to be the culprit as all connections had continuity.
So I guess that means the problem is between the ECU/EPM plug and the MAF plug. I loathe cashing that kind of stuff down, I'd much rather just splice in new wire straight from the computer's plug to the sensor.
Q: are there any duplicate color coded wires on the engine harness? (Besides maybe red and black) I want a 2nd confirmation of some sort I have the right pin/wire before cutting anything to splice in the new wire.
Yes, Ford used same color coded wires in different systems, but PCM shouldn't have duplicate color coded wires for devices
But you would find same colors in wiring for lights or radio or ect.....................
A full list, most sensors or controls have multiple codes the PCM can choose from, the codes PCM does NOT use can tell you as much as the one it DID use
Example for IAT/ACT air temp sensor codes
P0109 Intake Air Temperature Circuit Malfunction
P0111 Intake Air Temperature Circuit Range/Performance Problem
P0112 Intake Air Temperature Circuit Low Input
P0113 Intake Air Temperature Circuit High Input
P0114 Intake Air Temperature Circuit Intermittent
P0114 would for sure be a bad connection, might be sensor itself but bad/loose connection would be my first choice
Same for P0112, low signal could be corroded connection
That would make sense
The bare wire is the MAF sensor and MAF sensor data is compared to IAT sensor data so one low would make the other high when compared
Gasoline's air/fuel mix is 14.7/1 and this is a WEIGHT ratio not volume
14.7 POUNDS of air to 1 POUND of gasoline, or 14.7 grams of air to 1 gram of gasoline
This is why "pre-vaporizers" and 200 MPG carbs were/are a MYTH, lol, just FYI
A MAF sensor is used to get the WEIGHT of the incoming air, not "air flow" as its called, the computer, in your case, already knows its running a 4 LITER engine, so it already knows exactly how much air is coming in at any RPM, its just math
What the computer doesn't "know" is how much the air weighs because this changes quite a bit with elevation(height above sea level) and air temp, "hot air rises" because its LIGHTER than colder air
So MAF and IAT are used together in the same calculations
That would make sense
The bare wire is the MAF sensor and MAF sensor data is compared to IAT sensor data so one low would make the other high when compared
Gasoline's air/fuel mix is 14.7/1 and this is a WEIGHT ratio not volume
14.7 POUNDS of air to 1 POUND of gasoline, or 14.7 grams of air to 1 gram of gasoline
This is why "pre-vaporizers" and 200 MPG carbs were/are a MYTH, lol, just FYI
A MAF sensor is used to get the WEIGHT of the incoming air, not "air flow" as its called, the computer, in your case, already knows its running a 4 LITER engine, so it already knows exactly how much air is coming in at any RPM, its just math
What the computer doesn't "know" is how much the air weighs because this changes quite a bit with elevation(height above sea level) and air temp, "hot air rises" because its LIGHTER than colder air
So MAF and IAT are used together in the same calculations
I understand that. (Came from a DSM background, so I'm used to thinking about airflow in lb/min) And I get that the newer OBDII computer probably has something of a VE table to reference when in open loop operation.
What it sounds like you're getting at though, is while there is continuity at the plug, if the resistance from the corroded/oxidized wires is likely effecting the signal values, and could still be the culprit. I'm not very familiar with these vehicles so I don't know how sensitive it would be to something like this. I suppose I could see what the resistance is between the plug pin and about 1-2 inches down the wire from the plug, I wouldn't expect to see anything above a few ohms.
Anyone know off the top of their head what gauge the wires in question are? If I had to guess I'd say 14ga?
Last edited by Ziptie Mechanic; Apr 5, 2020 at 11:54 AM.
I checked resistance like I mentioned, in a few inches from the plug, there practically wasn't any unless you went to a 200 ohm scale and then it was still low, but what the heck that connector needs to be replaced by the look of it.
Old plug
New plug, which was attached by a solid soldering job and heat shrank the connections. I did one wire at a time so as to not cross any connections, worked from one side to the other until all done.
So new MAF, new plug, disconnected the battery to clear the codes, waited 5min or so with the door open to suck up any power in the system. Reconnected started, no code, cool....but, last time I didn't get a CEL, until the 2nd start up, so I let it idle for a few minutes and then shut down, restarted annnd just as I was about to celebrate, CEL lights up.....
Suggestions?
Last edited by Ziptie Mechanic; Apr 12, 2020 at 03:45 PM.
P0102 Mass or Volume Air Flow Circuit Low Input
P0113 Intake Air Temperature Circuit High Input
Drive it and see what running issue show up, should be other codes showing up
Only thing in common is a 5v reference but not shared in sensor just in the loom
And same 5v is used by TPS and ECT sensors
So you may have a computer issue, you already replace the MAF./IAT and connector so thats all thats left, well wire loom too
Already had 1 wiring issue. Which was resolved by just bypassing the harness and running a new lead from the ground of an injector to a few inches away from the pin on the computers plug.
So my money's on wiring. The larger red wire I presume is the 5v to the MAF? I'll check that tomorrow if this storm doesn't blow my house away.
Seriously, this is Ga, not Oklahoma! What the crap!?
The larger red and black wires are for the MAF heater, should be 12v on the red wire
Volt meter hooked to red and black wires should read battery volts, key on
Ford MAF is a "heated wire" sensor
A wire is heated up and the "sensor" reads how much it is cooled by incoming air, this measures the WEIGHT of the air not the temp
2 wires for the heater
2 wires for the wires temp sensor
And in your case 2 more wires for a separate IAT sensor
I have tan/light blue wire as pin 36 for MAF sensor return
Then light blue/red to pin 88
The 2 MAF sensor wires
Red and black wires are for the MAF heater, 12v and ground respectively
Then IAT(ACT, air temp) use
Grey/red wire which is a shared wire with TPS, ECT, ISS, OSS and a few other sensors, 5volt, from pin 91
Grey wire goes to pin 39 signal wire
Pin 28 is transmission solenoid D, brown/orange wire
I looked at a few years and did not see 28 used for MAF
What year is your truck if you don't mind me asking RonD? I'm just wondering if your wiring should be the same as mine.
I'll check the greywire with red stripe to see if it has 5v today when I get home as well as check the larger red wire for 12v and the ground.
So red wire gave 12v, so that's good.
The far left wire in the pic above of the grey wire with red stripe only showed 0.02v not running but key on. It did so consistently as soon as I touched the lead it showed .02v so it wasn't a fluke. But yeah that's definitely not 5v. But I should be able to splice into one of the other 5v sensors listed and just jump a wire straight to that lead/pin/wire on the plug then right? Because I'm not tearing apart wiring harnesses. I will tear into one though and properly spice, solder and heat shrink connections.
Also, right now public libraries are closed.
Last edited by Ziptie Mechanic; Apr 13, 2020 at 02:41 PM.
Did you use the Black wire as the ground when testing the red wire?
Its important, a loose ground means not really 12v at MAF heater
Yes the grey/red stripe wire is found on several sensors like TPS, ECT and DPFE
Test for 5v but you should have multiple codes if not 5v at the other sensors
