Problem with 2005 Buick Rendezvous ECM:

Solving 2005 Buick Rendezvous ECM (engine computer) problem is no easy task. One ATS customer suspected that the ecm was causing code P0335 and he asked for the vehicle ecm wiring diagram. A couple of days later he emailed me that the ecm reference 12v supply was missing which only read 2 volts. The ecm pin reference voltage supplies a 12 v to the crank sensor. When tested, the crank sensor pin also read 2 volts.

Testing the ignition switch wirings, he found that the power going in from the fuse was OK and the power going out to the ecm and ignition module was OK too. This led him to think that the ecm was faulty. He confirmed it by checking the ecm power and ground supply pins which were reading normal. He contacted ATS to confirm if his diagnosis is fine and wanted to know if changing the ecm is OK. The ecm cost about 1k from the dealer (ouch!)

Diagnosis for 2005 Buick Rendezvous ECM:

After verifying the wiring diagram, it seems that he made a correct analysis when testing the ecm. For example: if you test the power supply of the ecm, you should get 12v all the time when you turn the key on , engine off. The normal ground reading to the ecm should not be higher than 0.250 v again at key on, engine off. Once this is established, it is just a matter of testing the reference voltage which in this case is 12v as shown in the ecm wiring diagram.

Please note that on most other vehicle ecms, the reference voltage is 5 v. Therefore, since the 12v supply from the ecm reference v is responsible for supplying power to the crank sensor, the engine should start once 12v is fed to the crank sensor. Please remember, if the crank sensor does not get this 12v signal from the ecm, the ecm will not be able to make the crank sensor works.

Final fix for this 2005 Buick Rendezvous ECM:

As soon as my customer got this information, what he did was to run a fused jumper wire direct to the crank sensor terminal pin. The 2v supply problem was eliminated and the engine fired up. Since the ecm was expensive too. he was able to run the engine with this jumper wire saving him lots of money.

More Tips for 2005 Buick Rendezvous ECM:

1.) Using a jumper wire like this is not recommended by ATS. However, if the cost of the ecm is $1k, I would not hesitate to do it as long as it is your own vehicle. I hate to find out if it happens to somebody else vehicle and the mechanic who did it will not accept the consequences of his actions. Example, the ecm internal driver might be affected causing problems elsewhere.

2.) when getting the source of the jumper wire in this case, make sure the feed is a control feed source. This means the sources will only get hot or trigered if you turn the key on. This means not hooking it direct from the battery positive terminal.

3.) Unless you have the ecm wiring diagram, this analysis might be difficult to the reader. But once you are a member, ATS can tell you exactly the pin terminal designations of the ecm and crank sensor.

Thanks,

Richard