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[Solved] AUDI Q7 3.0 TDI - P0700 Gearbox Control Module Error & Intermittent Firing Issues

artsan1974 24366 15
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How can I fix an Audi Q7 3.0 TDI that intermittently won’t start, flashes the glow-plug light, and shows P0700 gearbox control module error?

The intermittent no-start was ultimately caused by water getting into the computer/ECU [#17325849] Before that was found, the useful advice was to diagnose the car while the glow-plug light is flashing, because the gearbox may be blocking start-up based on live selector/gear-position data even if it stores no fault codes [#17242056][#17243954] It was also suggested to check CAN communication, brake-pedal information, and any pending codes, and to log rail pressure while cranking when the fault is present [#17242056][#17242821] If the starter cranks normally, the gearbox itself is less likely the direct cause, and the flashing glow-plug lamp points more toward an engine-side control/input problem than a transmission fault [#17242482]
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  • #1 17241399
    artsan1974
    Level 10  
    Posts: 9
    Rate: 11
    Hello everyone, I am asking for help with my AUDI q7 3.0 tdi engine bug, the problem is, a month ago in the morning I took my daughter to school and parked for 5 minutes, after returning, the spiral flashes suddenly and it did not fall off, the tow truck and to my brother's workshop after Connecting the computer, the error code p 0700 gearbox control module popped up, all day of checking and nothing like the spiral flashing all day long, it is strange that in the morning I come up and here the spiral goes out and the engine started, I took the car and drove it for 2 to 3 weeks without any problems , the day before yesterday the spiral flashed suddenly and it does not start again, but I closed twice and created the ignition switch and the spiral went out and it fired, I will add that there are no errors in the box, I checked all the contacts under the shaft, I changed the sensors on the ramp and on the pump, please help me, I miss already ideas. I repeat the topic, if anyone has any ideas about my problem I will be grateful.
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  • #2 17242056
    Anonymous
    Anonymous  
  • #3 17242351
    artsan1974
    Level 10  
    Posts: 9
    Rate: 11
    The starter is spinning like crazy, there are no errors in the gearbox, the only error is in the p 0700 engine (mechanical damage to the gearbox controller), but there is something that the spiral is flashing, the fuel pump in the tank does not supply at this point, I will be honest with you that I bought the car with a damaged engine, before I bought the second engine, it was open all winter in the open air, then I bought a complete engine and as I mentioned after my brother had installed the engine for about a month and a half, I drove without any problems, hence the replacement of sensors from the worn engine,
    My suspicions are there not a motor driver because this is what the mechanic who works for my brother suggests. I will say that I drive with AUDI on a daily basis, only with my heart on my arm, the spiral flashes, I close the ignition switch and it goes out and I start only, I am afraid that it will be left on the road again.
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  • #4 17242482
    Anonymous
    Anonymous  
  • #5 17242499
    artsan1974
    Level 10  
    Posts: 9
    Rate: 11
    As I mentioned, the sensor on the rail is replaced, high pressure also and the shaft position sensor is New original with the rest of the engine speed shows the computer, I only did not check the camshaft position sensor, I even did so with the computer, I delete the error p 0700 and I start to disconnect the ankles from the sensors teeth he threw an error p 0700 but none of this error pops up, I even unfastened the cube from the box controller under the passenger seat and fired to be sure if the gearbox has something in common, it is strange that when it starts I can drive all day and nothing happens, it does not tug evenly it comes with strength, only when I turn it off, I wonder if the spiral will flash or not.
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  • #6 17242657
    bodzio012
    Level 33  
    Posts: 1888
    Help: 161
    Rate: 779
    When not smoking, can you connect to the engine without any problems? If so, no ECU.
  • #7 17242694
    Strumien swiadomosci swia
    Level 43  
    Posts: 27479
    Help: 1404
    Rate: 6402
    If your car does not go out while driving, don't mess with the engine accessories.
    From what you write, there is no power after turning on the ignition.

    If this happens to you, do not turn off the key, just call an electrician with a computer, let him connect and diagnose, and you will see what the commune is with and where the errors are.
  • #8 17242821
    Anonymous
    Anonymous  
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  • #9 17243905
    artsan1974
    Level 10  
    Posts: 9
    Rate: 11
    Hello, as I mentioned, my brother has a workshop, so I have constant access to a computer, the error comes out in the engine only p 0700, the situation is strange, but what you say, the pressure on the ramp will be checked and let you know, it's worse that it can be cool a few days and a few days on one day the spiral flashes times.
  • #10 17243932
    Strumien swiadomosci swia
    Level 43  
    Posts: 27479
    Help: 1404
    Rate: 6402
    When there is a fault, check the gearbox mode and position.
    I suppose she doesn't know what condition she is in and she won't let it start.
  • #11 17243950
    artsan1974
    Level 10  
    Posts: 9
    Rate: 11
    As if on the board I have P ... and no problem with the connection to the engine. There are no fault codes in the gearbox.
  • #12 17243954
    Strumien swiadomosci swia
    Level 43  
    Posts: 27479
    Help: 1404
    Rate: 6402
    It's not about errors, just the state of the box at the time of not firing.
  • #13 17243971
    artsan1974
    Level 10  
    Posts: 9
    Rate: 11
    I did not check this, but when the spiral is flashing and it did not come off, I tried to move the lever to the rnd etc. And return to the p. And nothing at all.
  • #14 17244075
    Anonymous
    Anonymous  
  • #15 17244094
    artsan1974
    Level 10  
    Posts: 9
    Rate: 11
    A friend can explain in a simple way how should I check the position of the box? And if you have enough, thank you for the advice so far, there is no fault program ...
  • #16 17325849
    artsan1974
    Level 10  
    Posts: 9
    Rate: 11
    Hello, I am happy to inform you that my problem with firing Q7 has been solved, the computer was at fault, water got into it.

Topic summary

✨ The discussion revolves around an AUDI Q7 3.0 TDI experiencing a P0700 gearbox control module error and intermittent starting issues. The user reports that the glow plug indicator flashes, and the vehicle fails to start intermittently, despite the starter functioning properly. Various components, including sensors and the engine control unit, have been checked or replaced, but the problem persists. Suggestions include examining the communication between the gearbox controller and other sensors, checking the fuel pressure, and ensuring the gearbox position is correctly recognized. Ultimately, the issue was resolved by identifying water damage to the computer, which was causing the faults.
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FAQ

TL;DR: Audi Q7 3.0 TDI no‑start with P0700 and a flashing glow plug? CR TDI starts at approx. 250 bar rail pressure; "Minimum rail pressure during cranking should be 250 bar." Diagnose live data during the fault, then verify selector, brake, CAN, and ECU power. [Ross-Tech Wiki — Diesel CR TDI: No Start] Why it matters: This helps Audi Q7 3.0 TDI owners and techs fix intermittent cranking-no-start without guesswork.

Quick Facts

What does code P0700 mean on an Audi Q7 3.0 TDI?

P0700 indicates the transmission control module requested the MIL. It’s an informational code in the engine ECU. You still need to scan the transmission module for specific faults. If no TCM codes appear, check CAN communication and start‑interlock inputs. [P0700 — Transmission Control System (MIL Request)]

Can a flashing glow plug light cause a no‑start on VAG diesels?

Yes. On VW/Audi diesels, a flashing glow plug lamp doubles as a general engine fault indicator. It can flag issues like brake light switch, throttle control, DPF sensors, or ECU power faults. Some faults can inhibit starting until conditions are correct. [Flashing glow plug light on TDI — causes and fixes]

If the starter cranks, is the gearbox the issue?

Unlikely. As one expert put it, "When the starter turns, the gearbox is not a problem." Focus on engine ECU power, fuel pressure, and sensor inputs instead of the transmission. Confirm live data while the symptom is present. [Elektroda, bodzio012, post #17242657]

Which live data should I check when the fault is active?

Log rail pressure during crank, engine speed (G28), cam sync (G40), brake pedal status, and selector position. Also watch TCM presence on CAN. "Check the pressure on the rail while turning the starter." Capture pending codes before clearing anything. [Elektroda, Anonymous, post #17242821]

How should I diagnose it when the glow plug light is flashing?

  1. Do not switch the ignition off; keep the fault present.
  2. Connect VCDS/ODIS and read live values and pending codes.
  3. Crank while logging rail pressure, RPM, selector, and brake inputs. Cycling the key can clear transient states and hide the cause. [Elektroda, Strumien swiadomosci swia, post #17242694]

What rail pressure should I see during cranking on the 3.0 TDI?

Expect about 250 bar minimum during cranking. If pressure stays well below that, diagnose the lift pump, HP pump, pressure control valve, leaks, or air in fuel. Use VCDS Measuring Values while cranking to confirm. This threshold often separates start vs. no‑start. [Ross-Tech Wiki — Diesel CR TDI: No Start]

Could crankshaft or camshaft sensors cause this intermittent no‑start?

Yes. A faulty G28 crank sensor can show zero RPM during crank, preventing start. A failing G40 cam sensor can cause sync issues. Monitor RPM and cam sync while cranking. Replace sensors only after confirming with data. [Elektroda, Anonymous, post #17242482]

Why does cycling the ignition sometimes clear the light and allow a start?

Key cycling can reset temporary fault states or reinitialize modules. That may briefly mask a root issue like weak rail pressure, marginal sensor signals, or ECU power glitches. Capture data before cycling, then fix the underlying cause. [Elektroda, artsan1974, post #17242351]

How do I check if the selector or brake interlock blocks starting?

Read live selector position from the TCM and brake pedal status from the engine or ABS module. The TCM must report Park or Neutral, and the ECU must see the brake pressed. If either signal is missing, starting can be inhibited. [Elektroda, Anonymous, post #17242056]

My TCM shows no errors. Can it still stop the engine from starting?

Yes. Self‑diagnosis can pass while interlock inputs are invalid or missing. Incorrect selector position or missing brake signal can still block a start. Verify those parameters and CAN communication when the symptom is present. [Elektroda, Anonymous, post #17242056]

Is unplugging the TCM a valid test on the Q7?

It is not recommended. In this thread, the engine still started with the TCM unplugged, but that is not a reliable test. It can trigger limp modes and mask the root cause. Use live data instead. [Elektroda, artsan1974, post #17242499]

What ultimately fixed the Audi Q7 in this thread?

The engine ECU had water ingress. Repairing or replacing the ECU resolved the intermittent glow plug flashing and no‑start. Inspect the ECU housing and connectors for moisture and corrosion before replacing sensors. [Elektroda, artsan1974, post #17325849]

Which scan tool should I use and what modules should I scan?

Use VCDS, ODIS, or equivalent. Scan Engine, Transmission, ABS, and Gateway. Read pending and stored codes, then log rail pressure and key interlock inputs during cranking. Focus on data while the symptom is active. [Ross-Tech Wiki — Diesel CR TDI: No Start]
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