All the fuses check out

All the relays check out

Could I have a faulty ignition switch? Or an open somewhere?

How do I go about troubleshooting this?Error Message

It cycles through all the protocols, finds none and fails to communicate.

What could be responsible for this and how do I go about solving it?

2000 Mazda MPV with anti-theft

I have access to the Factory Service Manual

I can find my way around electricity and electronics

I have a multimeter which I have used extensively in the past to solve a multitude of electrical faults on the vehicle

I suspect the ignition switch firstly and the anti-theft module secondly

Any ideas? Anyone?

Studying the PCM pinouts seems to indicate that there are just two DLC pins connected directly to the PCM and they are: PCM pin 5 to DLC Terminal 10 and PCM pin 79 to DLC Terminal 7



1 Answer 1



Courtesy of a SNAPON document

If the scan tool does not receive data from an OBD II vehicle

TEST 1: Connect the positive DMM lead to DLC pin 4 and the negative DMM lead to the negative battery terminal, using jumper wires if necessary. Do not connect to body or chassis ground but to the battery terminal directly

With the ignition on, voltage drop across the ground terminal should be 0.1 Volts or less

TEST 2: Repeat for DLC pin 5

NOTE: An open circuit or high ground resistance means that the PCM will never enter diagnostic mode.

TEST 3: Voltage check on DLC pin 2.

PCM transmits data on this pin

Connect the positive DMM lead to the class 2 Serial Data pin and the negative DMM lead to either pin 4 or pin 5 or a known good ground

With the Ignition on, voltage on the class 2 serial data pin should be 5V or fluctuating between 3.5V and 5.0V, If open, PCM cannot transmit data to the scan tool


Connect positive DMM lead to DLC Battery + terminal Connect negative DMM lead to battery ground terminal

It should read battery voltage

This tests the ECM Voltage supply as no power may be caused by a blown lighter fuse

TEST 5: Connect positive DMM lead to either DLC bias terminals Connect negative DMM lead to the ground terminal

With the ignition key ON and no bus activity, BUS + should read 0V BUS should read 5V

With the ignition key ON and bus activity, the voltage should vary from 0 to 5V depending on the amount of bus activity!

ADDITIONAL NOTES PCM receives battery voltage (B+) through a fuse or fusible link. Check for an open circuit. An open ground or power (B+) circuit on a fuel-injected engine removes power from the ECM and prevents the engine from starting.

ADDITIONAL INFORMATION: Old PCM is roasted, see attached picture when attempts are made to communicate after fixing the wiring problem Scanner response after fixing the wiring problem

With the new PCM, it works!

The fuse box aka Power Panel was no good. Replaced it and PCM was able to receive power as well as communicate via the K-Line!

Test 3 above does not apply to a Mazda MPV!

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .