ISRydr

Error Code P1128

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First let me Thank everyone who contributes to this forum. Without all of your help guys like myself would be in a world of hurt. I do paruse this forum for hints and tips but unfortunately I don't post until I have issues or problems and I'm back with still yet another problem. I have owned 3 Lexus' in total, the first two, a 95 LS400 and a 01 LS430, both were amazing cars and I"m totally a Lexus freak. But I currently have a 99 LS400 that has been a pandoras box of problems for me and I'm not sure the end is in sight.

I've had throttle and idle problems since day one and finally was given an error code of P1128 which I'm told means Throttle Control Motor Lock Malfunction. The cone shaped attachment on the right side of the throttle body was making a loud whirring noise the other day and with the motor running I tapped it with a wrench and the idle increased and the whirring ceased.

My mechanic, who is a Lexus certified mechanic, said he'd never seen that code and would need to do some research before telling me what needed to be addressed. I'm concerned that I will have to replace the whole throttle body.

Does anyone have experience with this code? and if so could you share what I can expect?

Thanks in advance for the help!!

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I wish you luck with your problem. I was just impressed to hear the mechanic was goin to research the code. Sounds like you found a good one. May your repair be inexpensive.

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If your mechanic has the correct diagnostic equipment he should be able to locate the exact problem but the information below should help with the throttle motor,TPS and pedal sensor.

The code suggests a conflict of information between the 3 components, I would start with the Pedal sensor as they have been known to fail on other vehicles.

Sorry about the layout below it was the way it pasted.

3. INSPECT THROTTLE CONTROL MOTOR w/ CLUTCH

(a) Disconnect the throttle control motor w/ clutch connector. ( B) Using an ohmmeter, measure the motor resistance be-

tween terminal 1 (M+) and 2 (M–).

Motor resistance: 0.3 – 100 Ω at 20°C (68°F) If the resistance is not as specified, replace the throttle control motor w/ clutch. (See page SF–43) © Using an ohmmeter, measure the clutch resistance be-

tween terminal 3 (CL–) and 4 (CL+).

Clutch resistance: 4.2 – 5.2 Ω at 20°C (68°F) If the resistance is not as specified, replace the throttle control motor w/ clutch. (See page SF–43) (d) Reconnect the throttle control motor connector.

4. INSPECT THROTTLE POSITION SENSOR

(a) Disconnect the throttle position sensor connector. ( B) Using an ohmmeter, measure the resistance between ter-

minals VC and E2.

Resistance: 1.25 – 2.35 at 20°C (68°F) If the resistance is not as specified, replace the throttle position sensor. (See page SF–43) © Reconnect the throttle position sensor connector.

1

3

4

Ohmmeter

VC

E2

Ohmmeter

B01727

2000 LEXUS LS400

(RM717U)

Author��: Date��: 1353SF–38

SFI – THROTTLE BODY

Ohmmeter

VC

E2

B01728

5. INSPECT ACCELERATOR PEDAL POSITION SEN- SOR

(a) Disconnect the accelerator position sensor connector. ( B) Using an ohmmeter, measure the resistance between ter-

minals VC and E2.

Resistance: 1.64 – 3.28 at 20°C (68°F) If the resistance is not as specified, replace the accelerator ped- al position sensor. (See page SF–43) © Reconnect the accelerator pedal position sensor connec-

tor.

6. REINSTALL V–BANK COVER

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Thanks for the info Steve. I was watching when my mechanic pulled up the code and his scanner actually said it was a Throttle Control Motor Lock Malfunction. I've not been able to personally determine what that means exactly and because of the whirring noise coming from the cone shaped attached to the right of the throttle body I won't take a chance by taking on a trip through the Christmas holiday for fear of getting stranded. My question is, with the noise I heard coming from the motor or clutch is that repairable? Or does that signify my potential need to purchase anouther throttle body? I've seen prices for a new throttle body and I'm panicking thinking I'll have to shell out that kind of money then add labor etc. I haven't been able to locate a used TB that visually looked like I would take a chance and buy it. Is there a source for good used parts of this type?

I really appreciate your help!!

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The car uses "Drive by Wire" technology so relies on various inputs from various sources to know where the throttle pedal is and how open or closed the throttle butterfly is.

The motor controls the throttle butterfly opening and closing so if an input to the ECU is missing or incorrect the motor may as you describe be randomly moving trying to find the correct position.

The main input as I mentioned is the Accelerator/Throttle pedal position sensor, if this is defective or misadjusted it may well cause the problem.

Reading a fault code should only be taken as a guide to assist fault finding, it is not an exact science so good old fashioned checks with a multimeter need to be done also when investigating.

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Ahhh...makes sense now Steve. I will pass this info on to my mechanic, who probably is already on top of what to check for, but it never hurts to be involved.

Thanks again!! Merry Christmas to you and yours!!

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Steve, thanks for the post. My 99 LS400 just acted up tonight. Check engine light, VSC off warning, drove ok for about 3 minutes then leaving a stop light the throttle had no response. Luckily the 98-00s still have a throttle cable and will crack the throttle open at about 3/4 throttle so I was able to limp out of traffic. Did a restart and the same warnings but the throttle was working again. Pulled the code, P1128 and just now pulled up this post in response.

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On 8/6/2013 at 10:36 PM, JBrady said:

Steve, thanks for the post. My 99 LS400 just acted up tonight. Check engine light, VSC off warning, drove ok for about 3 minutes then leaving a stop light the throttle had no response. Luckily the 98-00s still have a throttle cable and will crack the throttle open at about 3/4 throttle so I was able to limp out of traffic. Did a restart and the same warnings but the throttle was working again. Pulled the code, P1128 and just now pulled up this post in response.

Having the same issue. Any fix? Ty

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