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Ask Chris (aka-Moose) Your Own Question
Chris (aka-Moose)
Chris (aka-Moose), Technician
Category: Car
Satisfied Customers: 1176
Experience:  16 years of experience
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The nature of it... Im not in front of the car diagnosing it

Customer Reply

Customer: replied 9 years ago.
1999 Lexus ES300. Codes P0171, lean bank 1, P0325 Knock 1 and P0330 Knock 2. No overdrive. Poor acceleration. VSC light on. Switched A/F sensor. Used donor knock sensor bank 2. No change.Replaced ECM, no change. Have been told there is a wiring harness problem. Research indicates knock sensors causing problem but not sure of how to fix. Require definitive answer from someone that has dealt with this problem. Thanks
Expert:  Auto Tech Guy replied 9 years ago.


Definitive answer? Anything on a website like this is always "best guess," thats the nature of it... I'm not in front of the car diagnosing it... I dont know what else could be happening with it. It would be negligent of me to say "oh yeah its this!" at best I could say "its probably this!" That being said.

No overdrive or VSC= Normal, when you have a CEL they shut off

I think that it may be a good possibilty that there is a harness issue IF you replaced the ecu and knock sensor of a *known* good one.

Going forward with that knowledge its time to start performing some tests:

Causes of knock sensor failure->

 Open or short in knock sensor 1 circuit

 Knock sensor 1 (looseness)


Testing knock sensor:

Using an ohmmeter, check that there is no continuity between the terminal and body. If there is continuity, replace the sensor.


Time to check at the ecm if the knock senosor signal is even getting to the ecm:

Both are in connector e11 and are in PINS 27 and 28 (refer to above below)

It should be a pulse generated signal and would be best to have an occilliscope read the signal, if you have a good enough voltmeter it may have the function.

-If your test leads are long enough test for resistance over the wire, inside the engine comartment to the ecu terminal

*hint* back probe the ecm terminal with a needle or long bobby pin

I believe your going to find a break in the harness and will need to replace/repair it BUT CHECK IT FIRST. It is shielded wire, so dont put standard wire back in place of it if you do.


Good luck, I hope this helps. Good day.


-Auto Tech Guy