longbeard

I’m troubleshooting a 2001, Camry 2.2L for Codes P0105 and P0401 and would like to know if anyone can confirm the following figures are correct for the MAP sensor.


According to Haynes 97-01 Toyota Camry Manual PG(6-11)


(3) Using a voltmeter and suitable probes, back probe connector terminal 2 with the positive probe and terminal number 1 with the negative probe – Turn ignition switch on (engine not running).
(4) Apply vacuum to the sensor and verify voltage from the signal wire-


.03 to .05 volts @ 3.9 in-Hg
.07 to .09 volts @ 7.8 in-Hg
1.1 to 1.3 volts @ 11.8 in-Hg
1.5 to 1.7 volts @ 15.75 in-Hg
1.9 to 2.1 volts @ 3.9 in-Hg


MAP Wiring question

Terminal 1 Ground
Terminal 2 Carries voltage/vacuum signal from MAP to PCM/PIM, .03 to 2.1 volts
Terminal 3 Carries the reference voltage from the PCM to MAP, 4.5 to 5 volts


With the connector disconnected, Should terminal 2 have power flowing to the map or is it only charged by Terminal 3?


Thanks

Brian R.

Welcome to the AF!

The ECM provides voltage to MAP - no connection, no voltage on terminal 2. That is why you have to back-probe the connector to check the voltage on terminal 2 when you apply a vacuum.

http://i16.photobucket.com/albums/b8/rogersb/MAP.jpg

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longbeard

Thanks Brian R

I was afraid you were going to say that. If what you’re telling me is correct (it explains a lot), Haynes needs to add another step to the test procedure to prevent a false reading of the MAP sensor.

After checking the reference voltage on terminal (3) and terminal (1), (connector disconnected) you should check for power by connecting the positive probe to terminal (2) and negative probe to terminal (1) and / or suitable ground to verify there is zero voltage.

If zero voltage if found proceed by checking the MAP signal voltage by back probing T(2) positive and T(1) negative.

But wait, looking at the diagram you posted (on the ECM side) it appears MAP terminals (3) and (2) are connected by a resistor symbol and both are fed by a 5-volt source with T (1) being the ground. In other words it appears just the opposite of your explanation, am I reading the schematic wrong?

This is what I have at this point (I’ll retest later using different test procedure and post result).

Connector side (disconnected)

T(3) to T(1) is 4.5 volts
T(2) to T(1) or ground is 3 volts

Back probe T(2) and T(1) vacuum results

MAP # 1

3 volts @ 0 in-Hg
3.25 volts @ 4 in-Hg
2.5 volts @ 7.8 in-Hg
1.85 volts @ 15.75 in-Hg
1.45 volts @ 19.75 in-Hg

Active codes P0105 and P0401
EGR system checks out ok

MAP # 2

3.00 @ 0 in-Hg
2.75 @ 4 in-Hg
2.00 @ 7.8 in-Hg
1.75 @ 15.75 in-Hg
1.5 @ 19.75 in-Hg

Active codes P0401
EGR system checks out ok

Conclusion faulty PCM or wiring problem due to 3 volts on T(2)

What's your opinion on it?

longbeard

Ok retested the system with T(2) connector out of the loop by Jumping T(3) and T(1) at the sensor/connector. Applied vacuum and took readings from MAP T(2)and T(1) both MAP readings matched the previous set.

At this point the only thing I can conclude is we have improper test information or the 3 volts on T(2) from the PCM damaged both MAP sensors, in which case I’m looking at at-least two faulty components / problems.

Again I’m working on my 2001 Camry 2.2L and would like to confirm the proper MAP sensor test. If anyone could double check their manual (other than Haynes) or run this simple test procedure on a 2001 Camry 2.2L I would really appreciated any and all help.


Brian R I’m not suggesting your wrong I’m just trying to rule out all the possibilities. PCM’s and MAP sensors are just a little on the expensive side.

Also keep in mind that I don’t have a P0105 code with sensor #2, but do with sensor #1.

Thanks again

Brian R.

I don't understand. Is this your proposal for the manual? If you are suggesting that one should test the voltage on the connector (ECM) side of the circuit when the connector is apart, there will always be voltage to terminal 2 of the ECM when the connector is apart and the ignition switch is on, since it is connected to terminal 3 by a resistor. If you are saying that one should test terminal 2 of the MAP side of the connector, faulty MAP or good MAP, there will never be voltage across terminals 1 and 2 of the MAP with the connector apart. There is no power.

Quote:

Originally Posted by longbeard But wait, looking at the diagram you posted (on the ECM side) it appears MAP terminals (3) and (2) are connected by a resistor symbol and both are fed by a 5-volt source with T (1) being the ground. In other words it appears just the opposite of your explanation, am I reading the schematic wrong?

My previous post only answered your question about the presence of a voltage difference between terminals 1 and 2 on the MAP side with the connector together and apart. I said nothing about the voltage apparent on the ECM side. There will always be voltage on the ECM side of terminals 3 and 2 with the ignition on.

The description of the expected voltages in the Haynes manual is incorrect. The voltages listed are not the expected voltages as Haynes states they are, they are the voltage drops expected from the reference voltage. Haynes does not even tell you to measure the reference voltage correctly. They call the ECM supply voltage to the MAP sensor (Terminals 3 and 1) the reference voltage which is incorrect. The reference voltage is the voltage between Terminals 2 and 1 with the vacuum line disconnected and the connector attached and the ignition key "ON" (see below).

With the connector attached and the ignition on and the vacuum line disconnected, measure the reference voltage by backprobing terminals 2 and 1. Measure the voltages at these same connectors while applying different vacuums at the port. If your reference voltage without vacuum is 3 volts (for example), then you should see the following voltages at these vacuums:

3.94 in Hg 2.5-2.7 V [3.0 V (reference voltage) minus 0.5-0.3 V]
7.87 in Hg 2.1-2.3 V (3.0 minus 0.9-0.7 V)
11.81 in Hg 1.7-1.9 V (3.0 minus 1.3-1.1 V)
15.75 in Hg 1.3-1.5 V (3.0 minus 1.7-1.5 V)
19.69 in Hg 0.9-1.1 V (3.0 minus 2.1-1.9 V)

Apparently this is what you have done, without knowing that you needed to subtract the given voltages from the correct reference voltage to get your test target voltages.

Since your MAP #1 shows 3.25 V at 4 in Hg, It appears it is bad. That is higher voltage than the reference voltage (3.0 V) when it should be lower. Recheck your measurement, but it appears your DTC with this MAP confirms it is bad. Replace the MAP if this is a real measurement.

Although the output from the second MAP is not exactly what is listed above as the ideal voltages, the trend is the same and I would assume it is good. Perhaps you didn't measure the reference voltage exactly correctly. This would bias all the measurements equally and in one direction. I don't think there is anything magical about these absolute numbers as long as they are close to the above ranges, it is having a smooth trend that is important. There is bound to be some variation with altitude.

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Brian R.

Here's the procedure from the Toyota service manual:

http://i16.photobucket.com/albums/b8...5S-FEMAP-1.jpg

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longbeard

Quote:

Originally Posted by Brian R. I don't understand. Is this your proposal for the manual? If you are suggesting that one should test the voltage on the connector (ECM) side of the circuit when the connector is apart, there will always be voltage to terminal 2 of the ECM when the connector is apart and the ignition switch is on, since it is connected to terminal 3 by a resistor.

Misunderstanding, it was a proposal only if terminal 2 of the ECM side was not suppose to have power when the ignition switch is on.

Quote:

Originally Posted by Brian R The description of the expected voltages in the Haynes manual is incorrect. The voltages listed are not the expected voltages as Haynes states they are, they are the voltage drops expected from the reference voltage.

Great! You identified the problem as far as the Haynes manual is concerned. I’m sure that’s not their only mistake, you might want to add this one to your sticky.

With us being into it this far would it be possible for you to post the Toyota test procedure for the EGR system?

Quote:

Originally Posted by Brian R. Haynes does not even tell you to measure the reference voltage correctly. They call the ECM supply voltage to the MAP sensor (Terminals 3 and 1) the reference voltage which is incorrect. The reference voltage is the voltage between Terminals 2 and 1 with the vacuum line disconnected and the connector attached and the ignition key "ON" (see below).

It looks like they are calling Terminal E2 - Terminal 1 and Terminal VC - Terminal 3, which would be the "reference voltage" / power source voltage 4.5 to 5.5 volts. What They are calling Terminal 2 is the same as the PIM. Therefore the reading from PIM to E2 would be the output voltage. OK just wanted make sure I'm on the same page.

Please excuse the poor image quality, el-cheapo camera.
http://i105.photobucket.com/albums/m...eardnc/map.jpg


Thanks

Brian R.

Forget Haynes for this issue. Replace the MAP sensor, pull the battery cables to reset the ECM and see what happens.

For the EGR troubleshooting procedure, reference the link to the Gen 4 manual in the sticky post at the top of this forum.

http://oregonstate.edu/~tongt/camry/...on_Control.pdf

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longbeard

Yea its pretty bad when you have to troubleshoot a repair manual. The new MAP sensor fixed the P0105 problem, I just wanted to verifiy the test procedure and rule out it was the cause of the P0401. Still have a P0401 after reset but thats another story.

Thanks for all the help.