Engine/Transmission (1998.5 - 2002) Code 234 Issue

[BMelhuish]

I just bought a new scanner. After doing a lot of work to the fuel system that included a DDRP Lift Pump, replacing the fuel filter, fixing the leaking fuel heater, and installing a Issopro fuel pressure guage, the truck runs better than it ever did. But, I just couldn't leave it alone. I hooked up the scanner for a test run.

It gave me a P0234-Turbo Over Boost. I have no, nada driveability issues. The MAP sensor was replaced in May together with the Crank Shaft Positioning Sensor. I cleared the codes and went on a test drive. I drive very conservatively. So, this time I stepped on it. No power loss at all. RPMs almost redline through all gears with no loss of power or dead pedal issues. Fuel pressure never went below 10 psi.

I know that turbo over boost can either be the Map Sensor or the Waste Gate sticking. I thought an over boost would result in the computer shutting off fuel. Hence, loss of power or dead pedal. I do not have a boost gauge to see what the boost actually is. I checked for codes again after my test drive and got the same code. I have not checked for a stuck waste gate, but I don't have any symptoms of it either.

Why then am I getting this code? Bad MAP Sensor? Thanks for your help.

 

[VolsFan]

On my dads 99 work truck, the over boost code was thrown on it years ago. It is stock. It was also blowing a lot of smoke too and boost was low.Took the map sensor out and cleaned it with carb and choke cleaner and never got the code again, and that has been at least 200k hard miles ago, nearing 500k now

 

[DavidC]

I had that code also. Bought a new map sensor and the code came up again. I found the wires chafed at the sensor at the end of the convoluted tube. Repaired wiring, no code since.

Dave

 

[BMelhuish]

I hadn't thought of the wiring or just cleaning the MAP. So, so I'll check the wiring and clean the sensor. I'll also check the waste gate operation. I'm rather new to all of this code stuff and appreciate the help. Thanks.

 

[SAndreasen]

My 01 always through that code after I put the chip on went almost 300 000 before i got rid of it never had a problem

 

[BMelhuish]

Since I cleared it and the code came back on my test drive, I want to check out every possibility before I dismiss it. I think I understand that codes are not the end all and often further diagnostics are necessary to determine whether an issue exists or not. So far I have no symptoms of what this code could represent. As an aside and if it is important, I did get the companion code P1693. I understand that code just tells me that another code exists.

It was dark, windy and cold last night. So, I haven't followed up on your suggestions yet.

 

[BMelhuish]

Here is the answer that we believe is correct. I found absolutely nothing wrong with the truck. Waste gate operation was perfect and nothing was wrong with the MAP sensor or wiring. Since I couldn't find a thing wrong, I took it to the mechanic that I use for such things. He too found nothing wrong. He did find several TSBs that dealt with the issue. When you replace parts of the fuel system with aftermarket products, they may not perform within the parameters set in the PCM or ECM thereby triping the code. The DDRP pumps substantially more fuel and at greater pressures than the stock pump. The shop manual lists the OEM pressures at 10 psi at idle and not less than 6 running. The DDRP does 17 at idle and not less than 11 psi at any time running. Just going down the highway at 70 mph, it does 14 psi. Apparently, there is no issue. So, unless symptoms develop, I'm not going to worry about it. I should have thought to get the TSB numbers.

Thanks for your help.

 

[JR]

Your fuel pressure is actually closer to where its supposed to be, the OEM pumps are not capable of supplying adequate volumes of fuel. Anything over 14psi and the overflow valve opens at the VP and dumps back to the tank. It will not set any codes.

 

[BMelhuish]

I dunno. All I know is that I have a code and no symptoms or apparent problems. I reported the lift pump pressures from the Dodge shop manual. As to reading and using the diagnostic codes, I'm pretty much in the bottom half of the learning curve. Something is setting the code. But in my case there seems to be nothing to fix. In short and despite the code, the turbo and MAP are operating properly and within specifications. So, until and unless a problem develops, I'm leaving it alone for now.

 

[JLandry]

...I have a code and no symptoms or apparent problems....

the turbo and MAP are operating properly and within specifications.

Couple of questions (sorry if they've been answered already and I missed it):

1. Did this code start coming only AFTER you installed the new MAP sensor back May, or was it happening prior to that and the replacement was an attempt to correct it?

2. During your recent troubleshooting, has the boost pressure actually been measured (i.e.: does your truck have a boost pressure gauge permanently installed or was one added temporarily for testing purposes)?

3. Has the current MAP sensor been tested using air pressure and a multimeter to verify it has the correct output?

Thanks,

John L.

 

[BMelhuish]

John L.

I'll address your questions as presented.

1. I have no idea. In May 2013 a "Check Engine" light came on. This was before I started doing my own work again. I took it to a shop that I do not usually use. They advised that it needed both CPS and MAP sensors and installed them for me. I assume without knowing that all codes were cleared and that they pertained only to those components. At the time I didn't really perceive any driveability issues. Shortly after that repair, however, I started having issues with the torque converter locking and unlocking. I fixed a battery ground and relocated the APPS wire from behind the alternator and solved that issue.

2. I checked the actuator operation, wiring to the MAP Sensor, etc. I found nothing obvious. I did not check the MAP sensor operation with a volt meter. I do not have a boost gauge installed or otherwise. So, I took the truck to my usual shop, told them what I had, and asked them to check it out. They reported that the turbo and waste gate were operating properly and that an overboost condition did not exist in their testing. I assume that they also checked the operation of the MAP. It had him stumped. Hence the TSBs that he found.

3. I found this on a whim. I was just trying to understand the operation of my new scanner, how to use and what information it would provide. I wasn't having any real issues. As an aside the passenger side battery went bad. I finally noticed it when it got cold enough here for the grid heater to kick on. It was replaced the Sunday before Christmas. Last Tuesday both grid heaters kicked on (it was really cold in Tampa-lol) and the alternator wasn't charging until the heaters shut off. Alternator was bad so I had the shop install a new one while they had it. They also really really cleaned the battery cables saying that they found a slightly bad positive connection on the driver side battery.

4. The truck does run very well. Under the circumstances, the shop's explanation is plausible. May be it was related to the charging system. I haven't checked to see if I still have the code.

Thanks,

 

[JLandry]

BMelhuish,

If I understand you correctly, you don't know for sure if you have a genuine over boost condition occurring, nor do you know if the current MAP sensor is functioning as it should. You really need to positively rule these things out through validated testing and not just assumptions.

If you don't mind throwing money at the problem rather than doing the testing, then you can swap out the current MAP sensor with a new one to try and rule out that as a problem, but that still won't confirm if an over boost condition is occurring due to something else.

Best regards,

John L.

 

[BMelhuish]

Not exactly. The shop reported that they tested the boost and that an overboost condition did not exist in their testing. They also examined and tested the wastegate and actuator and reported that they were fine and operating properly. Now, I (personally) only checked to see if the gate was sticking-it wasn't. I'm pretty sure that they did not pull the MAP sensor and test it. I pulled and cleaned it as suggested. I suppose that it could be bad and giving me a false code. But I'm not getting the voltage codes. So, no I don't know what the boost is doing on an on-going basis. The MAP sensor is fairly cheap, but so far it appears to be operating properly. At any rate the computers aren't doing anything with the code.

Is there anything other than the turbo wastegate that could cause an over boost condition? If I have this correct, if an overboost exists, the MAP is to send a signal to the PCM and the PCM shuts down or reduces the available fuel to bring the boost back within acceptable parameters. Can the MAP send the code (right or wrong) without the PCM shutting the fuel down?

Sorry for all the questions.

 

[BMelhuish]

Well, this is all pretty interesting. I hooked up my scanner and went to the view data screen. MAP is measured in inches of mercury on my scanner. Holy high school nightmares! At idle I got about 30 inches and at WOT I got 75 inches. I live at sea sea level, and we have some weather. So, 30 inches (or darn close) would be 1 ATM or 0 psi. 75 inches would be about 36 psi according to the google conversion. 1 ATM is about 15 psi. Substracting that from the 36 psi to get gauge pressure would mean that I'm getting 21 psi boost??? Do I have this even close?

The freeze frame when the code appeared indicates that I was at 94.9% throttle, 2516 rpm, 92.2% load, and at 40 mph. The inches dropped fairly rapidly back into the 30s.

 

[JLandry]

Without knowing the exact barometric pressure at the time of your test, it sounds like your math is reasonable to me.

John L.

 

[BMelhuish]

Thanks. Today the pressure is 30.17. I did purchase a MAP sensor today. Generally, the specs from dodge put the max boost at 17.5-18.5 psi +/- 1.5. I have not yet found any verified or reliable specs on what is considered an overboost and at what psi the code is thrown. I rounded off the figures, but I put the boost in the 21.5-22.0 range. Obviously, it is not high enough to defuel nor would I consider that to be an overboost. I'll put in the new sensor and see if the code clears or if I get different values. Interestingly, the manual tells you to use 21 psi to test the function of the wastegate.

Thanks for your help.

 

[BMelhuish]

I found the offender! The wastegate actuator is leaking badly. You can hear and feel the air rushing out of it. It is not working at all. I'll replace the actuator. BTW I found a TSB on this. Apparently, they have a repair kit. TSB 11-08-08. Hopefully, this is for the 24 valve HX35W too.

I initially only checked to see if I could move the wastegate. Yesterday, I bulit a handy pressure checking tool to check the wastegate and actuator operation. I have a small pancake compressor. I used 3/8s fuel line and installed some pneumatic connections with a pressure gauge in between so that I could hook it up to the compressor. I can also regulate the line pressure at the compressor. The manual says to test at 15-20 psi.

I took the pressure line off at the top simply because it's easier to get to. I used a fuel line fitting and clamped it with hose clamps. At least the issue is now known. I don't believe in coincidences and wasn't comfortable with the advice from my favored shop. So, as to further convince me that I should be doing these things myself, I decided to thoroughly check the waste gate operation. Wa-la problem found and solved.

 

[JLandry]

Glad you found the problem.

This sure doesn't speak well of your repair shop!

John L.

 

[BMelhuish]

JL:

It certainly does not. Thanks for everyone's help!

 

[BMelhuish]

Done. BTW Crysler makes an actuator repair kit. But. it's pricey-$260. It includes all of the gaskets that you'll need, nuts for the actuator, and an e-clip. All of the instructions are in the above referenced TSB. Virtually no measuring, gauges, etc. The boost is right where it should be. Cleared the codes, test drive, recheck for codes, and good to go.

The only PITA about the job is the bottom 2 nuts on the manifold. I tried everything from crows feet to universals. The only thing that I had that worked was a 12 point wrench. The nuts are tight, and there is no leverage. Anyone have any better way for the next time I need to take the turbo off?

Thanks again for all your help.