94 F150 MAF Sensor Code 157
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Junior User
Joined: Jun 2021
Posts: 84
Likes: 13
From: Michigan
94 F150 MAF Sensor Code 157
I've been dealing with this code for around a month. The truck is a project, not a daily.
Getting a code 157. Here's what's new on the truck.
IAC
Throttle Position Sensor
MAF Sensor
EGR
Fuel Pressure Regulator
I've only cleaned the Air Charge Temp Sensor because nobody local has one that will fit.
Code 157 Persists.
I have 12v at Pos+
I have 12v as Neg-
I ONLY have 6.18v on second groud going to PCM
Signal wire ok.
How do I fix this problem? Obviously the 2nd ground should also be at 12v.
I've researched this problem, it's not terribly common but it does happen....But the conversations always seem to end without a fix being unclear to the reader.
Any Help?
Getting a code 157. Here's what's new on the truck.
IAC
Throttle Position Sensor
MAF Sensor
EGR
Fuel Pressure Regulator
I've only cleaned the Air Charge Temp Sensor because nobody local has one that will fit.
Code 157 Persists.
I have 12v at Pos+
I have 12v as Neg-
I ONLY have 6.18v on second groud going to PCM
Signal wire ok.
How do I fix this problem? Obviously the 2nd ground should also be at 12v.
I've researched this problem, it's not terribly common but it does happen....But the conversations always seem to end without a fix being unclear to the reader.
Any Help?
Thread Starter
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Junior User
Joined: Jun 2021
Posts: 84
Likes: 13
From: Michigan
Yes, and it will keep coming back.
I think I'm about to call it a PCM issue. Unless I'm understanding wrong, the 2nd ground seems to be coming from the PCM? As mentioned in my Post. I have 12v on +/- when I get to the 3rd wire (second ground). I have 6.18v. It's my understanding that the line goes directly to the computer.
I'm testing the voltage by back probing the terminals in the KOEO position without the connector connected to the MAF.
I think I'm about to call it a PCM issue. Unless I'm understanding wrong, the 2nd ground seems to be coming from the PCM? As mentioned in my Post. I have 12v on +/- when I get to the 3rd wire (second ground). I have 6.18v. It's my understanding that the line goes directly to the computer.
I'm testing the voltage by back probing the terminals in the KOEO position without the connector connected to the MAF.
Lead Driver
Joined: Jan 2019
Posts: 5,086
Likes: 869
From: N.W. Alabama
Quick read how they fixed his post #10-->Codes 157 and 332 | Bronco Forum - Full Size Ford Bronco Forum
Hotshot
Joined: Jun 2015
Posts: 12,885
Likes: 2,448
Yes, and it will keep coming back.
I think I'm about to call it a PCM issue. Unless I'm understanding wrong, the 2nd ground seems to be coming from the PCM? As mentioned in my Post. I have 12v on +/- when I get to the 3rd wire (second ground). I have 6.18v. It's my understanding that the line goes directly to the computer.
I'm testing the voltage by back probing the terminals in the KOEO position without the connector connected to the MAF.
I think I'm about to call it a PCM issue. Unless I'm understanding wrong, the 2nd ground seems to be coming from the PCM? As mentioned in my Post. I have 12v on +/- when I get to the 3rd wire (second ground). I have 6.18v. It's my understanding that the line goes directly to the computer.
I'm testing the voltage by back probing the terminals in the KOEO position without the connector connected to the MAF.
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Junior User
Joined: Jun 2021
Posts: 84
Likes: 13
From: Michigan
I’m getting 6.18v on what’s referred to as the “2nd ground” in this article… also referred to as the letter C
Edit: yes, looks like it’s also called the MAF return
https://easyautodiagnostics.com/ford...sensor-tests-3
Edit: yes, looks like it’s also called the MAF return
https://easyautodiagnostics.com/ford...sensor-tests-3
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Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
The "2nd ground" goes to Pin 9 on the PCM. It is the Signal Return line for the MAF signal. You most likely have an open circuit between the PCM and the MAF meter.
That Tan/Light Blue wire equates to Pin C in that test.
Here is the MAF diagram (along with others). Look at the left side where the Mass Airflow Sensor is located.
That Tan/Light Blue wire equates to Pin C in that test.
Here is the MAF diagram (along with others). Look at the left side where the Mass Airflow Sensor is located.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Pull off the PCM connector then measure between Pin 9 and the MAF connector's Tan/Light Blue wire. Think of this circuit as a dedicated ground for the MAF signal.
Pin-out Diagram of the PCM connector:
Disconnect a battery cable, ground is suggested, before removing the PCM connector.
Pin-out Diagram of the PCM connector:
Disconnect a battery cable, ground is suggested, before removing the PCM connector.
Hotshot
Joined: Jun 2015
Posts: 12,885
Likes: 2,448
No. You are checking resistance in the wire rla stated how to do the test. Disconnect the battery. Disconnect the connector at the computer (PCM) and at the MAF meter. Measure the resistance by placing one probe on pin 9 at the computer and the other probe at tan/lt blue wire at the MAF connector.
Thread Starter
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Junior User
Joined: Jun 2021
Posts: 84
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From: Michigan
Ok, and what should the resistance be? Should it be 0?
And based on the number? What do I do to fix it?
I'm going to go out shortly and take a look, but I have my doubts that the actual wire is broken, it's still encased in its wire loom, wrapped tightly, and it doesn't look like it's ever been cracked open. I'm going to test it anyway, because you know what they say about assuming. So, once tested, then what?
And based on the number? What do I do to fix it?
I'm going to go out shortly and take a look, but I have my doubts that the actual wire is broken, it's still encased in its wire loom, wrapped tightly, and it doesn't look like it's ever been cracked open. I'm going to test it anyway, because you know what they say about assuming. So, once tested, then what?
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
As close to zero as possible since you are measuring a relatively short length of wire.
If the wire is open between Pin 9 and the MAF connector you could run a new wire or start pulling the loom off to find a break.
If the Signal Return wire measures good then take a good look at PCM connector Pin 9 for signs of corrosion. Do the same for the MAF connector. If those check out then I suggest you pull out the PCM then open it up to inspect for signs of moisture, burned components, leaking capacitors. You are already half way there by taking the PCM connector off.
If the wire is open between Pin 9 and the MAF connector you could run a new wire or start pulling the loom off to find a break.
I'm going to go out shortly and take a look, but I have my doubts that the actual wire is broken, it's still encased in its wire loom, wrapped tightly, and it doesn't look like it's ever been cracked open. I'm going to test it anyway, because you know what they say about assuming. So, once tested, then what?