1992 Lexus LS 400 Knock sensor

Tiny
SIERRASIERRA
  • MEMBER
  • 1992 LEXUS LS 400
Engine Performance problem
1992 Lexus LS 400 V8 209000 miles

Check engine light is indicating code 55 - #2 knock sensor, but I don't sense any pinging. How urgent is it to replace it? One of 2 knock sensors. Light comes on only sometimes, usually when I've left the car undriven for several consecutive hours or longer. Is there also a relation to how the engine is started? Start up can be whiny even though the starter motor is relatively new--whiny starts seem to cause the light to come on.
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Friday, June 5th, 2009 AT 10:47 PM

9 Replies

Tiny
MHPAUTOS
  • EXPERT
Hi there,

I would be getting the knock sensor replaced, you do run the risk of doing damage long term if this is not responding, you will also have poorer fuel economy and power problems, as for the starter, if it is noisy or spinning and not fully engaging I would get this attended to as well as it may start to damage the drive plate or at best fail and strand you.

Mark (mhpautos)
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Friday, June 5th, 2009 AT 10:51 PM
Tiny
SIERRASIERRA
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Any ideas on why the light is not always coming on? Does leaving it undriven for some consecutive hours do something to make it more prone to coming on?
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Friday, June 5th, 2009 AT 10:58 PM
Tiny
MHPAUTOS
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The light is just a visual indication that there is a problem that need attention, the set code in the ECU will remain there until the problem is resolved, when the ECU reads in put signals from the sensor it will log the code and set the light when the readings for the sensor is out of the normal parameters, this sensor may be failing spasmodically, I would still get it sorted ASAP.

Mark (mhpautos)
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Friday, June 5th, 2009 AT 11:04 PM
Tiny
SIERRASIERRA
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Since most of the repair estimate is on labor to get to the sensor, would you replace both at the same time?
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Friday, June 5th, 2009 AT 11:24 PM
Tiny
MHPAUTOS
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Hi there,

Yes I would, I had a smilier problem with my VW transporter, I change both sensors as a matter of course.

Mark (mhpautos)
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Friday, June 5th, 2009 AT 11:31 PM
Tiny
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Thanks, Mark, you have helped me to decide to change them.
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Friday, June 5th, 2009 AT 11:37 PM
Tiny
MHPAUTOS
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Hi there,

You have made the wise decision, thank you for using 2 car pros,

Good luck,

mark (mhpautos)
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Friday, June 5th, 2009 AT 11:49 PM
Tiny
SIERRASIERRA
  • MEMBER
My repair shop quoted me $700 in labor just to get to the sensors and put everything back. I found this entry in a Lexus site:

"You can change the knock sensors and wire harness without removing the intake manifold. Remove the EGR valve, PCV hose and you can get you hand into the V area of the block. A 27mm socket and small rachet with a flex head and the job is done."

If anybody with knowledge of the LS400 could confirm this, it would be appreciated.
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Saturday, June 6th, 2009 AT 12:11 AM
Tiny
MHPAUTOS
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Hi there,

I have never replaced one on this model my self, so I am unsure, but you post will remain active so someone who has done this may respond, I will check the time book to see what the recommended time is to do this job,

mark (mhpautos)
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Saturday, June 6th, 2009 AT 12:41 AM

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