Bad Map Sensor?

[Kalergie83]

Hi. 

I have the plug in G4+ for Toyota MR2. 

My mechanic has a problem with the MAP sensor. I initially had an AEM, the Voltmeter and Link software showed 0.02V. My Link dealer advised that MAP sensor is most likely faulty and we ordered a brand new Link MAP Sensor. Unfortunately, same problem. The mechanic even tested manually using 0.5bar pressure, which should have made the volt go up but nothing was moving. We are wondering what could be the reason since we are out of ideas. Could the new MAP sensor be bad as well? It would be the 2nd in a row?

All cables were tested for correct wiring and had 0 OHM impedance. According to the provided manual, the MAP sensor signal is on PIN34. 

I'd appreciate your advise. 


 

[Adamw]

Assuming you have the ST205 ecu, the MAP sensor can be connected to either AN Volt 3 (pin 37) or AN volt 4(pin 34) depending on model and region  Have you confirmed you have 5V and ground at the sensor?

[Kalergie83]

Thanks Adam. Yes, 5V and good ground confirmed. We will test with a MAP sensor that we definately know works. If that one works, it's the new MAP sensor that was faulty. But let's say it doesn't work. What other reason could there be? We are a bit out of ideas. Thanks

[Adamw]

So are you testing both AN V3 & 4?  The chances of 2 different MAP sensors from 2 different companies being DOA but outputting the exact same voltage is so slim I wouldn't even consider that plausible at this stage, there are so many other possibilities far more likely.  I dont know about AEM, but all our ones at least are tested before shipping.  

[Kalergie83]

Thanks Adam,

I will tell him to try both AN V3 and 4 (if he has not yet). I do know he used AN V4. But we should get a reading on the signal with a multimeter regardless which Pin it goes into, right? 
At this moment, 5V and ground is confirmed. Preassure hose used to pressurize 0.5 bar above atmosphere, no change on the multimeter reading. stuck at 0.02V. 

The other MAP sensor from AEM was very old and taken from a previous built. It made more "sense" that the AEM was faulty. Which is why we immediately assumed it was broken. But now the Link MAP sensor has the same problem.

 

[Kalergie83]

So my mechanic tested a generic Toyota MAP sensor and it shows that it works. Our Link dealer is insinuating that my mechanic initially installed the MAP sensor wrong (confusing + and ground). Is that even possible? Does it destroy the sensor if by some crazy accident, the mechanic confuses + and ground?

 

[Adamw]

Our MAP sensors are one of the few that are reverse current protected. And I dont think putting 5V into the signal pin would hurt it either.  About the only thing wiring-wise I think would damage it would be powering from 12V rather than 5V.  

[Kalergie83]

Hi Adam, 

Thanks. So we sent the MAP in to our LINK dealer, it was actually ok. So there is definately something wrong on our end. Just what could it be?

When pulling out the Signal cable out of the ECU, then signal out has 1.7V. 

When the MAP is connected correctly, then Signal out shows 0V and 0OHM. We dont think is correct, is it? My mechanic says this shows there is some sort of short circuit.

Can you see any indication that there is something wrong from a wiring perspective? 

 

 

 

[Adamw]

19 hours ago, Kalergie83 said:

When pulling out the Signal cable out of the ECU, then signal out has 1.7V. 

If you have a Link 4 bar MAP sensor its voltage output should be about 1.18V at atmosphere.  

 

19 hours ago, Kalergie83 said:

When the MAP is connected correctly, then Signal out shows 0V and 0OHM. We dont think is correct, is it? My mechanic says this shows there is some sort of short circuit.

It is not really clear what you are doing, but if you are saying your MAP sensor is outputting 1.7V when the signal wire is disconnected, but drops to 0V when the signal is connected, then yes, this would suggest that signal wire is shorted to ground somewhere.  

[Kalergie83]

Hi Adam,

Yes, it's 1.18V. 

Odd phenomenon my mechanics just observed. So the MAP sensor signal is on PIN 34 which is in the 16 PIN socket. When my mechanic pulls out the 26 PIN socket from the ECU but keeps the 16 PIN socket in, the MAP sensor is suddenly outputting 1.18V. When he sticks the 26 PIN socket back into the ECU, the MAP sensor is outputting 0V/0Ohm. So it appears that the 26 PIN socket interferres somehow with the 16 PIN socket or at least with PIN 34. Is there anything from your side that rings a bell? Something about the 26 PIN socket that we may have done wrong that could cause the PIN34 to go short circuit? 

Thanks.
 

 

[koracing]

The 26 pin socket is where the ECU is getting most of it's grounds (two left most pins, and the bottom right most pin usually). I can tell you it is highly advisable to not disconnect ground while the ecu is powered up.  It is very common on MR2s to get poor or bad grounds for various reasons, but if you ensure that you have a good clean, bare metal contact on the bottom of the intakd manifold where the engine harness attaches it's ground, and good bare metal contact for the heavy gauge ground wire from the top of the transmission to the chassis on the left side of the engine bay (again bare metal as in all paint cleaned off, and both ends of any cable connection cleaned/sanded) that usually will resolve any strange grounding issues.  With the engine off you can test all the brown wires in the 26pin connector to a good ground on the chassis and you should have very close to zero resistance.  Anything more than a few tenths of an Ohm says you're not grounding properly.

Beyond that other things on the 26 pin that may be of relevance: Distributor trigger connections, injectors, ignition output, idle control valve, Narrow band o2 heater, and EGR solenoid and TVIS solenoid, and OEM boost hi/low VSV.  Perhaps try disconnecting each of those items and seeing if any of those make a change to the MAP reading or if any are backfeeding voltage onto the ground circuit.  Assuming that fixes the signal, plug each thing back in one by one and see where the problem arises.