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Engages limp mode after head gasket change, how to fix?

Tiny
GEOGEO123
  • MEMBER
  • 2008 TOYOTA COROLLA
  • 4 CYL
  • 165,000 MILES
Hello, I have the car listed above S. I changed the head gasket last week, reason, I was driving and suddenly the car overheated, upon inspection I found coolant mixed with the motor oil) and now the car has engine code P2103.

After replacing the head gasket and putting the car back together I topped off the oil and added water instead of coolant for testing. I drove the car and it would not accelerate past 25 MPH. Before taking it to a shop I check compression and got around 170psi on all four cylinders. I also checked spark plugs, coils, and fuel injectors and they all passed with a multimeter. I took it to a shop where they told me I had a bad throttle body, and the exhaust manifold was cracked.

I replaced the throttle body with an Oreily part, and the car was reset at the shop. The car drives fine for 2-3 minutes and then engages limp mode again not going past 25mph, I can turn off the car and it will repeat driving fine for a few minutes and then engage limp mode. If I put on the old throttle body, it won't accelerate well for a few minutes like it does with the new part. What could be the issue?
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Tuesday, July 18th, 2023 AT 2:07 PM

8 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,269 POSTS
Hi,

The problem is likely in the wiring. The code indicates a high voltage issue with the throttle actuator control motor. Chances are we have a short to power and the motor is seeing 12v all the time. Also, when this code is set, the PCM puts the vehicle in limp mode to protect the circuits. That is normal for this issue.

If you look below, I attached the diagnostics for the code. Take a look through them and let me know if you are comfortable performing them.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what you find.

Joe

See pics below.
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Wednesday, July 19th, 2023 AT 9:01 PM
Tiny
GEOGEO123
  • MEMBER
  • 5 POSTS
Hi, thanks for the response. I will grab my multimeter and check this out tomorrow in the afternoon, currently close to midnight, and report the results here!
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Wednesday, July 19th, 2023 AT 9:45 PM
Tiny
GEOGEO123
  • MEMBER
  • 5 POSTS
Hello, I disconnected the negative terminal on the battery and ran my test. I specifically ran the test for a short by grounding and then checking resistance on the throttle body connector, I got no change in the multimeter, aka it kept reading 1. Both T6-2 and T6-1 had no change.

I then jumped into the car and checked the ECM connector. This one felt tricky since the image was upside down when viewed from my angle, but I think I checked it correctly and found the black and white wires to check respectively. These wires also had no change (kept reading 1 on my multimeter).

Would the next step be to change out the entire wire? Or to maybe replace the throttle body connector? I moved the wires around on the throttle body connector while testing to see if maybe it was just loose but still had no change in resistance.

Thanks!
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Thursday, July 20th, 2023 AT 10:48 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,269 POSTS
Hi,

It could be either. Is the connector in good condition? Can you pierce the wire to see if there is a difference before the connector?

Joe
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Thursday, July 20th, 2023 AT 6:26 PM
Tiny
GEOGEO123
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  • 5 POSTS
The connector is in good condition, I pierced it just now and no different before the connector.
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Thursday, July 20th, 2023 AT 7:14 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,269 POSTS
Hi,

when you say it stayed at 1, was it at one when not connected? Also, if you had the battery disconnected and checked it as mentioned, you were checking for a short to ground. Was that your goal?

Let me know.

Joe
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Friday, July 21st, 2023 AT 7:10 PM
Tiny
GEOGEO123
  • MEMBER
  • 5 POSTS
Hi, yes it stayed at 1, and correct I was checking for a short. Well long story short I figured it out, the fault was a lose ground wire near the top of the engine. (I must have forgotten to fully tighten a bolt holding a ground wire when I was putting the engine back together from the head gasket job).

More detail: I ended up double checking the throttle body connector for both a short and an open thinking I might have done it wrong after watching more YouTube videos. The wires seemed to pass both tests, so then I followed the mechanics recommendation which was to try an OEM throttle body (I had already ordered the part days back but was waiting for it in the mail). The mechanics reasoning was it didn't like the aftermarket part. So, I did that and tried a used OEM part, that didn't work either, the car went immediately into limp mode.

After scratching my head and staring at the engine for about an hour I decided to turn on the car and just wiggle wires and air pipes around to see what would happen. Eventually I noticed the car would shutter, and even turn off, when I moved a group of wires on the right side of the engine, near the throttle body. I finally narrowed it down to a lose ground wire. I tightened it up and the car started up right away with no check engine light, test drove it around and all is good!

Thanks for the help!
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Sunday, July 23rd, 2023 AT 3:59 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,269 POSTS
Hi,

Thanks for the update. That is an easy thing to miss. However, I'm glad you found the issue.

If you have questions in the future, feel free to come back anytime.

Take care,

Joe
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Sunday, July 23rd, 2023 AT 6:36 PM

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