Not getting 5 volt power from ecm

Wodiesel04 · May 12, 2016

2001 Mazda b3000 5speed . Recently replaced heads , injectors and ECM chasing a misfire issue . Finally got the truck going has good compression , starts right up and idles and drives around town fine . Took it on the hwy and it started running like crap . Pulled a p1121 and p0102 code . Checked the grey/red 5v power wire and am only getting half a volt . Where do I look now

hoosier1104 · May 12, 2016

Check your PCM relay and ground for the engine bay fuse box.

Wodiesel04 · May 12, 2016

Not to sound dumb , but if the relay wasn't working wouldn't the ECM be getting no power at all ? Are you referring to the large eyelet ground on the front of the fuse box ? Lastly what about the ECM diode in the fuse panel what role does it play ? Thanks for the help

RonD · May 12, 2016

The Gray/red stripe wire is also connected to the ECT sensor, Intake air temp(IAT) sensor(with MAF), EGR DPFE sensor, clutch/trans sensor.

So must be a local issue, or you would be getting other codes, test voltage at the other listed sensors.

The code 0102 is generated because MAF sensor voltage is to low for the RPM the computer is seeing and not changing, check connector.

1121 is generated because when throttle is opened, TPS voltage rises, MAF sensor voltage is not changing, so MAF and TPS do not match, which would indicate, like 0102 does, that voltage isn't changing on MAF

I would retest voltage on top wire of TPS using a sewing pin to pierce the wire while it stays connected, key on.

Also test ECT sensor wire, and DPFE sensor wire, also IAT sensor wire, one of the outside wires on 6 wire MAF connector

Wodiesel04 · May 12, 2016

I checked the voltage at all the sensors you mentioned except the clutch/Trans sensor ( didn't know where it was ) all sensors read the same .5 to .6 volts at the Grey/red wire . Even probed the grey/red wire directly at the ECM connector and I get the same .5-.6 volts everywhere

Wodiesel04 · May 12, 2016

Btw when I'm checking voltage I'm going from the grey/red wire to battery negative . Should I be going to the tan/white ECM ground wire on the sensor

RonD · May 12, 2016

One my EEC-V diagram I have
Pin 89 Gray/White = TPS sensor
Pin 90 Brown/White = Ref Voltage
Pin 91 Gray/Red = Signal Return

Look at other Pin Outs and they have the same, just different wire colors on some

Try the Brown/White, or tan/white wire

Wodiesel04 · May 12, 2016

Ok all the PIN numbers and wire colors match what you stated in the above post , but the only wire that the ect,egr,intake temp and tps sensors have in common is the grey/red . So wouldn't that mean that the grey/red was the 5v signal wire ?

RonD · May 13, 2016

No, it could be the "ground", not really a ground but a known voltage.
5volts isn't 5volts unless you have a known 0volts.
And because these sensor's return voltage need to be accurate computer needs to control or "read" both.

Wodiesel04 · May 13, 2016

Thank you for all the help , got the issue sorted out it was a bad mass air flow sensor

RonD · May 13, 2016

Shorting out the voltage?

Thanks for the update

Not getting 5 volt power from ecm

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