HELP! (No power to OBD2/Stereo/Interior Lights/Multiple CIL's/More Details Inside)

mazda6780

Member
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2005 Mazda 6i 2.3L (Hatch)
Hi All,

I have pasted a thread that I had started at 6crew.com below in hope that someone here can help me. The folks at 6crew.com have been extremely helpful however this thread had hit a dead-end with no resolution. If anyone can shed some light on this situation, I would be extremely glad. I really do not want to start parting out my poor 6 :'( . If you require any additional information, please do not hesitate to ask. I am no pro, but am semi-mechanically inclined and am willing to try anything at this point. The post below explains the exact situation. Thanks in advance guys!

I recently had trouble with an over-charging alternator which, fried my battery as a result. While everything in the car ran normally, the transmission continued to go into safe-mode, however ALL electronics worked. I had put a new battery in tonight just to move the car to the garage while searching for an alternator, only to find that the AT, Traction Control, Check Engine and Battery lights were all illuminated. Also, the stereo, interior lights do not function as well as the gauges do a full sweep when starting. Upon checking every fuse in the car, I had noticed that the only blown fuse was the TCM fuse. I had replaced it, however it immediately blows on ignition (just switching to ON will trip it). The car WILL start and drive, but only in what appears to be third gear (no gear indicator). Also smells to be running very rich. Would anyone know what the problem might be? All other fuses appear to be fine. My car is a 2005 Mazda 6i 2.3L (Hatch) with just around 100,000KM on the odometer. Any help you all could give would be greatly appreciated. Thanks in advance!

**EDIT**

Also, the keyfob does not unlock/lock the doors, and internal locks do not function unless the ignition is in the ON position.

**Updates**

Official List:

Not Working:
Stereo
OBD2 Port (No Power in any key position)
No PRND indicator (I would guess this is due to the TCM fuse being blown, the car will go into gear with a clunk and drive, but it is definitely in safe mode)
No Gear Indicator (Same as above)
Central Locking and Electric Windows (These will only work if the key is in the ON position, engine started or not)
Interior Lighting (Does not work in any key position)
Engine seems to be running rich due to potent gas smell from exhaust.
AT Light is on
Traction Control Activation light is one. (However TCS OFF is not, and I do have the ability to switch it on and off without issues)
Battery Light is on
Check Engine is on (Cannot pull codes due to no power to the OBD2 Port)
Dash lighting for stereo, shifter and AUTO button. Steering wheel buttons also do not light up.
Low Beams not working
High Beams not working
DRL's not functioning


Working:
Engine starts right up without any issues or hesitation
Gauges/Cluster (The gauges do work and appear to be accurate, however they do a full sweep upon turning the ignition on, and seem to be stuck in position when the vehicle is switched off. Upon turning the car on, they Max Out, do a full sweep and return to normal)
Cluster lighting
Electric Drivers Seat
Oddly enough the integrated fog lights work.
Fuel Pump primes as normal when the key is turned to ON.

Odd items to note:
When the key is turned off, there seems to be more relays cycling than normal.
When the high-beams are activated, I can hear the relay activate but they do not work.
Mostly the same result whether the engine is started or not, with the exception of the central locking not working unless the key is in the ON position.
NO OBD2 POWER!
A/C Line seems to frost over 1 minute after starting the engine.
Both cooling fans appear to be running constantly, starting from 30 seconds after engine start-up


Things Checked:
Starter (No difference when disconnected)
ALL Fuses with a VOM. Only the TCM fuse is blown and continues to blow.
Wiring in the engine bay appears to be intact and clean. I cannot see anything melted.
Cleaned battery terminals and connectors

So you tell me.... is this the end of the 6? I have just purchased a black 2011 Mazda 3 Sport GT (2.5L) to replace the 6 and love it, but I would love to have my 6 back on the road as well. This whole mission has been rather heart-wrenching. The 6 is in such good shape with no issues at all up until 103,000 KM. It has never missed a service. Again, you people are great, any help or additional advice you all could give would be greatly appreciated. Thank in advance!
 
There's fuses and relays for a reason, I wouldn't think any of the body or engine ecus got damage. It's likely blew fuses or wrecked relays. Maybe melted wires but I can't see it.

Take every fuse and relay out and test them. Relay testing procedures are in the service manual.

Also that fuse that you keep blowing. Look up the wiring schematics for that circuit and trace/test the wires. There has to be a short to ground somewhere to blow a fuse immediately.
 
Last edited:
There's fuses and relays for a reason, I wouldn't think any of the body or engine ecus got damage. It's likely blew fuses or wrecked relays. Maybe melted wires but I can't see it.

Take every fuse and relay out and test them. Relay testing procedures are in the service manual.

Also that fuse that you keep blowing. Look up the wiring schematics for that circuit and trace/test the wires. There has to be a short to ground somewhere to blow a fuse immediately.


Hey! Thank you for the quick response!! Ok, so I have tested every fuse in the vehicle, ALL fuses are good with the exception of the TCM fuse which consistently pops on Ignition ON. I have not checked the relays though. In the service manual, it states to check for continuity across different terminals. Can this be done without a 12V source? Am I just checking for continuity across the specified terminals with the relay in my hand and if I do not have continuity it is cooked? Also, can I attempt pulling a relay from a working system and placing it in a slot that I believe to be blown or are they different voltages? I am going to start this afternoon with the testing and will report back what I find. Thanks again!
 
OK! UPDATES!

After 4+ hours of rechecking ALL of the fuses and them all being ok, I had found loose wire on the BCM that connects the ROOM fuse. I have re-soldered this wire and replaced the ROOM FUSE. List of things currently working -vs- still not working below:

Working:
Stereo
Interior Locks
Remote Locks
Interior Lights
Fog Lights
High Beams
Tail Lights
Brake Lights
Gauges not sweeping anymore and working accurately
OBD2 Now has power and scanned is able to connect. Only code thrown is U0101 which is expected because the TCM fuse still keeps blowing.
Horn works again
Steering wheel controls and dash-lights work
Alarm Works

Not Working:
TCM Fuse still continually blows on Ignition ON
No PRND/Gear Indicater
AT, Traction Control Activated, Check Engine and Battery light still on
Engine Cooling fans come on roughly 10 seconds after engine is started and stay on constantly.
AC also appears to be constantly running, AC line frosts up almost instantly when the engine is started. Oddly enough, the AC is working thought and blowing colder than ever.

Odd things to note:

ALL signal light bulbs are blown
ALL low-beam bulbs are blown

Questions:

Does anyone know where the TCM module is located in the car, I would like to unplug it to see if the TCM fuse still blows to try to rule it out as an issue. Any advice would be greatly appreciated! Thanks to ALL!
 
Depending on the model, The tcm should be located on your transmission around the front under your intake pipe, or inside the car under left side of dash. The brown wire is the power wire coming from fuse. Disconnect the connector and check the brown wire for continuity to ground. If the wire is grounding replace it. If the wire is good then your tcm is bad and needs replaced.

Hope that helps! The only Mazda 6s I work on are manual and don't have a tcm. So I'm just going by the diagrams in shopkey, Which aren't the best.
 
Depending on the model, The tcm should be located on your transmission around the front under your intake pipe, or inside the car under left side of dash. The brown wire is the power wire coming from fuse. Disconnect the connector and check the brown wire for continuity to ground. If the wire is grounding replace it. If the wire is good then your tcm is bad and needs replaced.

Hope that helps! The only Mazda 6s I work on are manual and don't have a tcm. So I'm just going by the diagrams in shopkey, Which aren't the best.

Hey, I checked above the tranny and didn't see anything.....going to try the left side next. I'm seeing in a downloaded service Manual that states it may be part of the PCM, however I have no idea what year the service manual is for. I am honestly hoping that this is not the case, I hear a new PCM is a depressing amount of money...
 
Hey, I checked above the tranny and didn't see anything.....going to try the left side next. I'm seeing in a downloaded service Manual that states it may be part of the PCM, however I have no idea what year the service manual is for. I am honestly hoping that this is not the case, I hear a new PCM is a depressing amount of money...

I am running into similar problems with my 03, 6. Mine has blown TCM, Hazard light, and power window fuses too.... Did you solved the problem???
 
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