Turbo Code Help 2007 XC70 - 126C: boost pressure sensor-signal too high

TempXCGuy · Post by **TempXCGuy** » 10 Aug 2025, 21:29

Hi, I have a couple of codes and a drivability issue related to the turbo. The car is a 2007 XC70 and the two codes are:
126C: boost pressure sensor-signal too high
601C: Turbocharger (TC) control system boost pressure fault - Signal too high

I have already replaced both the TCV and the MAP sensor, both were bad or highly questionable. But, I’m still getting these two codes. I am in the process of checking for boost leaks, just waiting for the smoke machine (I’m don’t think I have a leak, but I’m going to check anyway). Any other thoughts or things I could check?

Thanks in advance!

Post by **jonesg** » 10 Aug 2025, 21:52

waste gate actuation.
can you read the boost and vac ?

Vova585 · Post by **Vova585** » 10 Aug 2025, 22:00

At this point I would start with replacing/inspecting vacuum lines going to the waste gate actuator and TCV. IpD is selling great silicone hoses for this(i believe it was $20). If no leaks in the hoses, I would move to check if waste gate actuator is still working(hand held vaccum brake bleeder might be of help). Might want to remove waste gate connector and inspect if it moves freely. If you are already there you already inspected short upper turbo hose that goes to the Intercooler for cracks. If that all checked good...I would try to look for an oem wiring diagram and focus on MAP. I think it is a 3 wire sensor. Dont quote me, but i think it should be on 5v reference(1 wire), constant ground(usually 3rd) and sensor/feedback wire (2nd wire). At times you might get short to power or short to ground with those aging wires. Interesting if it is a hard fault vs occurring after several drive cycles. Great idea to smoke test everything. Good luck

Post by **abscate** » 11 Aug 2025, 04:08

What reader are using? Make sure the codes map to the correct Volvo code in Vida

TempXCGuy · Post by **TempXCGuy** » 11 Aug 2025, 13:18

jonesg wrote: ↑10 Aug 2025, 21:52 waste gate actuation.
can you read the boost and vac ?

I haven’t seen the waste gate actuate, but I can make it move with compressed air. I am seeing readings from my scanner while test driving, yes.

How do I test vacuum on these cars or what’s the best way?

TempXCGuy · Post by **TempXCGuy** » 11 Aug 2025, 13:24

Vova585 wrote: ↑10 Aug 2025, 22:00 At this point I would start with replacing/inspecting vacuum lines going to the waste gate actuator and TCV. IpD is selling great silicone hoses for this(i believe it was $20). If no leaks in the hoses, I would move to check if waste gate actuator is still working(hand held vaccum brake bleeder might be of help). Might want to remove waste gate connector and inspect if it moves freely. If you are already there you already inspected short upper turbo hose that goes to the Intercooler for cracks. If that all checked good...I would try to look for an oem wiring diagram and focus on MAP. I think it is a 3 wire sensor. Dont quote me, but i think it should be on 5v reference(1 wire), constant ground(usually 3rd) and sensor/feedback wire (2nd wire). At times you might get short to power or short to ground with those aging wires. Interesting if it is a hard fault vs occurring after several drive cycles. Great idea to smoke test everything. Good luck

Thank you for the information. I haven’t checked the hoses between the TCV and turbo and waste gate, but I will. Major noob question here (I’m just not that familiar with turbo cars), the line going to the waste gate provides pressure and not vacuum, correct?

I’ll check wires at the MAP. I have “mapped” the output on the MAP sensor on my scanner (Autel) and it is fairly consistent until I’m accelerating. Then it spikes and drops quickly, usually results in a code shortly there after and dump of most boost produced from that point forward. I should say, it spike, then stabilizes. I will monitor voltage as well though, I’ve been watching boost.

The waste gate does move freely, but again it’s under pressure and not vacuum.

Thanks again!

TempXCGuy · Post by **TempXCGuy** » 11 Aug 2025, 13:26

abscate wrote: ↑11 Aug 2025, 04:08 What reader are using? Make sure the codes map to the correct Volvo code in Vida

It’s an Autel MaxiCOM MK808S. Can you explain your last sentence please? Been a mechanic for a long time, but this is my first experience with a Volvo.

Post by **jonesg** » 11 Aug 2025, 17:19

TempXCGuy wrote: ↑11 Aug 2025, 13:24
Vova585 wrote: ↑10 Aug 2025, 22:00 At this point I would start with replacing/inspecting vacuum lines going to the waste gate actuator and TCV. IpD is selling great silicone hoses for this(i believe it was $20). If no leaks in the hoses, I would move to check if waste gate actuator is still working(hand held vaccum brake bleeder might be of help). Might want to remove waste gate connector and inspect if it moves freely. If you are already there you already inspected short upper turbo hose that goes to the Intercooler for cracks. If that all checked good...I would try to look for an oem wiring diagram and focus on MAP. I think it is a 3 wire sensor. Dont quote me, but i think it should be on 5v reference(1 wire), constant ground(usually 3rd) and sensor/feedback wire (2nd wire). At times you might get short to power or short to ground with those aging wires. Interesting if it is a hard fault vs occurring after several drive cycles. Great idea to smoke test everything. Good luck
Thank you for the information. I haven’t checked the hoses between the TCV and turbo and waste gate, but I will. Major noob question here (I’m just not that familiar with turbo cars), the line going to the waste gate provides pressure and not vacuum, correct?

I’ll check wires at the MAP. I have “mapped” the output on the MAP sensor on my scanner (Autel) and it is fairly consistent until I’m accelerating. Then it spikes and drops quickly, usually results in a code shortly there after and dump of most boost produced from that point forward. I should say, it spike, then stabilizes. I will monitor voltage as well though, I’ve been watching boost.

The waste gate does move freely, but again it’s under pressure and not vacuum.

Thanks again!

ok , a quick test , reach in and tug lightly on the rubber coupler sleeve that connects the turbo output to the charged air pipe that goes over the engine. They can get loose and blow off under boost, dumping the boost, then get sucked back into place again when the wastegate dumps the boost, you're non the wiser until you pull on the pipe and comes off.

If thats not the problem, robert spinner has a video about volvo turbo operation.

Post by **matthew1** » 11 Aug 2025, 17:37

jonesg wrote: ↑11 Aug 2025, 17:19 They can get loose and blow off under boost, dumping the boost, then get sucked back into place again when the wastegate dumps the boost, you're non the wiser until you pull on the pipe and comes off.

That's exactly what happened to my 850 in 2008. Took an hour at a gas station at night with the hood up to figure out what was going on.

Post by **matthew1** » 11 Aug 2025, 17:42

TempXCGuy wrote: ↑11 Aug 2025, 13:26
abscate wrote: ↑11 Aug 2025, 04:08 What reader are using? Make sure the codes map to the correct Volvo code in Vida
It’s an Autel MaxiCOM MK808S. Can you explain your last sentence please? Been a mechanic for a long time, but this is my first experience with a Volvo.

Codes come in two varieties (that I know of)... look at this page and you'll see what I mean https://www.matthewsvolvosite.com/volvo ... wer-codes/