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Author Topic: How to Troubleshoot a BAP/MAP Sensor Circuit  (Read 22221 times)
Joel5.0
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« on: June 09, 2009, 08:12:10 pm »

How to Troubleshoot a BAP/MAP Sensor Circuit

The following was a case I worked on months ago, the same Mustang I replaced the valve springs. After the springs were replaced and the engine was started, some problems showed up regarding idle control and driveability. The causes were ID'ed as a vacuum hose leak (the supply hose to the brake booster), a BAP/MAP failure (code 22) and a faulty TPS (code 23). The following procedure focuses on the code 22 failure and how to solve for it.

DESCRIPTION:

The BAP/MAP sensor is a 3-wire sensor with a 5 vdc VREF supply, a SIGRTN gound and the BP/MAP signal wire. Altitude or vacuum readings is read by the ECM using the frequency output of the sensor through the signal wire, and is measured in Hertz (Hz)… NOT voltage output. This is why either a DVOM/DMM that can read frequency (Hz) or a BP/MAP sensor tester adapter is required. The following procedure uses a DVOM/DMM with frequency measuring capabilities.




TOOLS/EQUIPMENT:

  • Digital Volt/Ohm Meter (DVOM) with the capability to read frequency (Hz).
  • OR
  • Use of the attached tables to verify BAP/MAP output.

PROCEDURE:

The following procedure is based on the fact that a code 22 is logged in the system.

  • Disconnect BAP/MAP sensor
  • Place key in IGN ON and check for voltage at the BAP/MAP connector pins with the DVOM, between the VREF and SIGRTN pins, if ~5 vdc are not present, change to COM probe to a good ground source and recheck VREF output, if 5vdc is not present you need to trace the VREF wire of the sensor.
  • If 5 vdc were present when the COM probe was changed to a good ground source, SIGRTN wire needs to be traced for an open condition.
  • VREF and SIGRTN circuits confirmed as OK, check BAP/MAP signal wire with the SIGRTN or ground reference point for voltage, 5 vdc = OK, 0 vdc = need to trace BAP/MAP wire for a short to ground or an open wire condition.
  • Turn IGN OFF and reconnect the BAP/MAP sensor, making sure you pierce the signal wire with the cloth needle or the piercing clip, and attach the (+) probe from the DVOM/DMM to it as shown.


  • Attach the DVOM/DMM COM probe to a good ground, turn IGN ON and check output voltage as shown





  • The voltage should be ~.34 vdc - .39 vdc. This output is not relevant to determine if the sensor is OK, but it is shown as an explanation of this circuit.
  • Now switch the DVOM/DMM selector to read frequency (Hz), the picture below shows the failing sensor with an output of 0.0 Hz. The obvious conclusion is that the sensor is kaput/fubar.


  • The following pictures show the output reading in Hz of the trusty KGU (Known Good Unit) I always keep in the shop for these cases.



  • As you notice, and using the BAP table provided previously, the 158.7 Hz output corresponds to an altitude between 0 and 1000 feet…. which is compatible for my neck of the woods. If you want to get a little technical, simply extrapolate the value read with the values from the table, and estimate the actual reading in feet above sea level.
  • The other table applies for the output when vacuum is applied (MAP sensor function)

Hope this helps anyone.



NOTE: A correction was made regarding the voltage reding of the MAP/BP signal wire. It should also be 5 vdc when measured IGN ON, sensor disconnected.



« Last Edit: November 04, 2010, 02:02:14 pm by Joel5.0 » Logged

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« Reply #1 on: August 02, 2010, 02:10:19 pm »

I'm test my map sensor like a bar because it is on a maf setup, i've the code 22, i've my 5 vdc reference and my ground, the ground ref is gray and red wire, my 5 vdc is on black and white wire, and my bar signal is on the green wire, my problem is when my sensor is unpluged i have 5 vdc on the bar signal wire on pigtail. i went on the pcm and unplugged the pin 45 , now i have 0 vdc on the sensor pigtail, but i've 5 vdc at the pcm pin 45, i don't understand. let me know
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Joel5.0
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« Reply #2 on: August 02, 2010, 04:17:06 pm »

Wire 45, or the BP/MAP signal will show 5 vdc. The MAP is a frequency or digital on-off signal that the sensor switches between the SIGRTN and VREF reference points.

BP/MAP to SIGRTN = OFF (low)
BP/MAP to VREF = ON (high)

Higher frequency = less vacuum or more atmospheric pressure

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ACRONYMS:
LUK  LMK  JIC  BTSTDTRT  YCYDYP  NFI-YTM  SPOBI, and the classic... DILLIGAS

'86 Mustang GT, X-303 cam, Holley DP 700, RG Tran., 289 Heads   Ford Smilie 2


Quote from: Joel5.0
The right to be stupid is inalienable for sure however, there is no such thing as a right to impose stupidity onto others
Great Thoughts will Overwhelm a Feeble Mind
There is never money to do it right, but there's always money to do it over.
Knowledge based on external evidence is unreliable.
He, who doesn't ask, does not deserve an answer.
A mind is like a parachute it only works when it is open.  (oldmanjoe)
If you can't explain it simply, you don't understand it well enough. (Albert Einstein)
Tuning on a Dyno for the track, is like swim practice in a bathtub.
I can explain it for you, but I can't understand it for you. (90lxcoupe)
The proof of understanding is the ability to explain it. (H. Torruella)
Ignorance is bliss, but stupidity is orgasmic.
Fraud and falsehood only dread examination. Truth invites it. (Samuel Johnson)
The chaotic resistance of the opponents leads to the conclusion that they are not prepared to meet the challenge. The problem is already much more psychological then technological. [Bojidar Djordjev]
Individuals are rational and humane... Crowds are reactionary and barbaric. (Jason)
The person who says it cannot be done should not interrupt the person doing it. –Chinese Proverb
Nothing sways the stupid more than arguments they can't understand - Cardinal de Retz
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« Reply #3 on: March 19, 2012, 08:55:08 am »

digging this thread up..got a code 22 seemingly out of nowhere...parked the car for the winter, no code 22...pulled the motor, put new h/c/i on, put it back in, now have code 22

mass air car

checked the voltage at the BP connector, verified 5v Vref and BP signal wire, and the Sigrtn is all good at the connector, key on, BP unplugged...

plugged in the BP sensor, pierced the signal wire, DVOM to ground, and got 4.32v

i do not have a DVOM that reads hertz...but by verifying the voltage at the connector is good, would it be safe to say the BP sensor is no good?

or should i be looking for something else?
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mikestang
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« Reply #4 on: April 09, 2012, 06:42:48 pm »

I would find a meter that reads HZ.  Since the MAP/BAP sends out a frequency that is a 50% duty cycle the volt average should be closer to 2.5.  (depends on if you have a rms meter or not) No matter what the vacuum on the sensor the duty cycle stays the same, just that ammount of times it switches from 5 to 0 volts increases or decreases, (aka Hertz)  You could see this waveform with a lab scope. But a new sensor may be cheeper that a meter that reads HZ, so maybe buy a new sensor and see if your code goes away.
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Joel5.0
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« Reply #5 on: April 09, 2012, 09:58:17 pm »

I would find a meter that reads HZ.  Since the MAP/BAP sends out a frequency that is a 50% duty cycle the volt average should be closer to 2.5.  (depends on if you have a rms meter or not) No matter what the vacuum on the sensor the duty cycle stays the same, just that ammount of times it switches from 5 to 0 volts increases or decreases, (aka Hertz)  You could see this waveform with a lab scope. But a new sensor may be cheeper that a meter that reads HZ, so maybe buy a new sensor and see if your code goes away.

For the DIY guy? .... that is accurate to a point. What if by any chance (as I have also experienced) he gets a bad BP/MAP sensor? Would it also make sense for him to spend $$ on a EEC (you know, the other option) even though it will not fix his problem? ......to find out about it later?.... and as I have too experienced with customers that simply justify a shortcut?

In today's automotive world a frequency meter is a requirement. Or didn't you know that even though pressure solenoids in a transmission can do an off-on state, they too fail under frequency control? Money I have saved my customers from unnecessarily rebuilding their transmission?  THOUSANDS! Is a $120.00 price to pay too high to get the correct info by comparison and possibilities?  Don't ...no.... specially when responsibility is on your back.... as it is on mine.
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ACRONYMS:
LUK  LMK  JIC  BTSTDTRT  YCYDYP  NFI-YTM  SPOBI, and the classic... DILLIGAS

'86 Mustang GT, X-303 cam, Holley DP 700, RG Tran., 289 Heads   Ford Smilie 2


Quote from: Joel5.0
The right to be stupid is inalienable for sure however, there is no such thing as a right to impose stupidity onto others
Great Thoughts will Overwhelm a Feeble Mind
There is never money to do it right, but there's always money to do it over.
Knowledge based on external evidence is unreliable.
He, who doesn't ask, does not deserve an answer.
A mind is like a parachute it only works when it is open.  (oldmanjoe)
If you can't explain it simply, you don't understand it well enough. (Albert Einstein)
Tuning on a Dyno for the track, is like swim practice in a bathtub.
I can explain it for you, but I can't understand it for you. (90lxcoupe)
The proof of understanding is the ability to explain it. (H. Torruella)
Ignorance is bliss, but stupidity is orgasmic.
Fraud and falsehood only dread examination. Truth invites it. (Samuel Johnson)
The chaotic resistance of the opponents leads to the conclusion that they are not prepared to meet the challenge. The problem is already much more psychological then technological. [Bojidar Djordjev]
Individuals are rational and humane... Crowds are reactionary and barbaric. (Jason)
The person who says it cannot be done should not interrupt the person doing it. –Chinese Proverb
Nothing sways the stupid more than arguments they can't understand - Cardinal de Retz
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« Reply #6 on: April 09, 2012, 10:15:53 pm »

 ,Agreed the correct tool is always the best option.  Diag is what I do for a living.  You are correct, I do understand.   
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