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Codes say Drive by wire throttle body but tests seem to conflict
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Resto_60
New User
Sep 15, 2024, 8:27 AM
Post #1 of 7
(333 views)
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Codes say Drive by wire throttle body but tests seem to conflict
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99 Pontiac Firebird
V6 3800
104,000
Problem is with my 99 Firebird V6 3800 with the drive by wire throttle body. Its at 104K miles in the last 3 months it received: plugs, wires, timing chain, cam sensor, crank sensor, oil pan, oil pressure sensor, fuel pressure regulator, and fuel filter. It was running well and all of a sudden I have a barely start or no start condition. When it starts its missing badly and the response to throttle input by popping and killing. When I attach a Xtool A30M scanner stored codes are :
P1120-99 Throttle position sensor circuit 1
P1220-99 Throttle position sensor circuit 2
P1221-99 Throttle position sensor 1-2 correlation
P1516 -99 Command vs actual throttle position performance
I have cleared codes and they return if I'm able to get it to start for a second. If it starts it kills almost immediately left alone or with gas pedal input.
If I turn key on and depress the accelerator pedal the throttle body valve follows pedal position smoothly to wide open. I have verified the connector ref voltage for both TP sensors is approx 4.3 Vdc. If I press the accelerator pedal the TP1 and TP 2 sensor output is swings from approx .5v to approx 3.1 Vdc. I have verified both TCS fuse ETC fuse are both good. It seems to me that the throttle body is working in spite of the codes. I have tried to follow the OEM manual P1120 troubleshooting but it is really tough with a third party non GM Tech scanner. The drive by wire throttle body is not available new. I have reseated the main ECM connectors.
I'm starting to wonder if it could be the cam or crank sensor but I don't understand why it wouldn't set different codes in that case.
Any ideas would really be appreciated?
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Hammer Time
Ultimate Carjunky
/ Moderator
Sep 15, 2024, 10:05 AM
Post #2 of 7
(325 views)
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Re: Codes say Drive by wire throttle body but tests seem to conflict
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A few questions..........
Have you checked thoroughly for any rodent damage in any of the harnesses?
Have you checked the reference signal while the engine is running or cranking as other sensors that share the 5v reference can be shorted and kill the reference voltage for other components under certain conditions.
Are you using a scan tool to monitor TPS voltages while the problem is occurring?
The throttle body has it's own module that communicates with the PCM through data lines so it can have it's own internal problems.
Have any connectors been recently replaced or rewired?
The P1120 indicate intermittent high voltage which could mean it goes open circuit momentarily.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Sep 15, 2024, 10:14 AM)
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Resto_60
New User
Sep 15, 2024, 3:33 PM
Post #3 of 7
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Re: Codes say Drive by wire throttle body but tests seem to conflict
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Thank you for time and insight.
I have checked for rodent damage, couldn't find anything.
I would check reference voltage running but it doesn't run more than 1-2 seconds and kills.
My Scan tool has spots for TP1 and TP2 but that section is blank. I don't know if its a issue with the Xtool A30M live data or does the engine need to be running for those live signals to work? I have sent a message to xtool but no response yet.
I have reseated the wiring connector for the throttle body control module at the gas pedal.
Only wiring repair was a map sensor wire was repaired 6 months ago. Plug was extracted and wire was sodered. Seems to still be connected.
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Hammer Time
Ultimate Carjunky
/ Moderator
Sep 15, 2024, 3:38 PM
Post #4 of 7
(303 views)
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Re: Codes say Drive by wire throttle body but tests seem to conflict
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I'm afraid you're good to need some better equipment to get to the bottom of this. It's most likely going to have to be diagnosed by analyzing the data stream to find the anomaly.
Remember, it only takes a split second glitch to set the code. Most tech would be using a lab scope to diagnose this.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Resto_60
New User
Sep 15, 2024, 3:57 PM
Post #5 of 7
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Re: Codes say Drive by wire throttle body but tests seem to conflict
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Volt meter shows a signal for TP1 and TP2. Im surprised if its a split second trip I would expect it to idle a little.
Is there anyone who repairs these darn drive by wire throttle bodies?
The other odd deal is the xtool has an actuation test but when I ramp it in 10% steps nothing changes the desired position, the actual position or any of the TP1 /TP2 sensor outputs. I assume the xtool actuator test is faulty but I dont have a similar car to prove this theory
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Resto_60
New User
Sep 15, 2024, 3:58 PM
Post #6 of 7
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Re: Codes say Drive by wire throttle body but tests seem to conflict
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Volt meter shows a signal for TP1 and TP2. Im surprised if its a split second trip I would expect it to idle a little.
Is there anyone who repairs these darn drive by wire throttle bodies?
The other odd deal is the xtool has an actuation test but when I ramp it in 10% steps nothing changes the desired position, the actual position or any of the TP1 /TP2 sensor outputs. I assume the xtool actuator test is faulty but I dont have a similar car to prove this theory
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Hammer Time
Ultimate Carjunky
/ Moderator
Sep 15, 2024, 4:00 PM
Post #7 of 7
(299 views)
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Re: Codes say Drive by wire throttle body but tests seem to conflict
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Like I said, you are not equipped to diagnose this properly and I wouldn't start throwing parts at it without a confirmed diagnosis.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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