P29AE

Reductant Injection Valve Control Circuit High - Bank 1

P29AE is a generic OBD-II powertrain diagnostic trouble code: Reductant Injection Valve Control Circuit High - Bank 1. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P29AE
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on, possible limp mode)
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What P29AE means

P29AE is stored when the PCM or diesel exhaust fluid (DEF) control module detects an abnormally high voltage or resistance on the control circuit for the reductant (urea/DEF) injection valve on Bank 1. The module monitors the electrical state of the valve driver circuit and compares it against expected values; a high-circuit condition typically indicates an open circuit or a short to battery voltage.

The reductant injection valve meters a precise quantity of DEF into the exhaust stream upstream of the SCR catalyst. If the circuit fault prevents the valve from operating, DEF dosing stops, the SCR catalyst loses its NOx conversion ability, and the system enters a derating or limp mode after a defined number of warm-up cycles as required by emissions regulations.

Diagnosis should start with a thorough electrical inspection of the injection valve connector, wiring harness, and the module output driver. Internal valve coil resistance should be measured and compared to specification. The control module itself is rarely at fault and should only be considered after all wiring and valve tests have been completed.

Common causes

Most-frequently reported root causes when P29AE is logged.

  • 1
    Open circuit in the reductant injection valve wiring harness or connector.
  • 2
    Corroded or backed-out terminal at the injection valve connector.
  • 3
    Reductant injection valve coil open internally, causing high-side resistance.
  • 4
    Short to battery voltage on the valve signal or power wire.
  • 5
    Defective DEF dosing control module output driver.
  • 6
    Chafed wiring routed near exhaust components causing intermittent opens.
  • 7
    Frozen or seized DEF in the valve body blocking normal electrical testing.

Symptoms drivers notice

MIL and/or SCR warning lamp illuminated.
Vehicle enters power derate or speed-limited limp mode after multiple drive cycles.
Increased NOx tailpipe emissions.
DEF consumption stops or becomes irregular.
Scan tool shows reductant injection commanded but no dosing confirmed.

How to diagnose P29AE

A typical diagnostic flow when this code is present.

  1. 1
    Record all active and pending codes; note any related SCR, DEF level, or NOx sensor codes.
  2. 2
    Inspect the Bank 1 reductant injection valve connector and wiring for corrosion, opens, or chafing damage.
  3. 3
    Measure injection valve coil resistance at the component and compare to manufacturer specification.
  4. 4
    Check for battery voltage on the signal or power circuit indicating a short to voltage.
  5. 5
    Perform a continuity test of each wire between the valve and the control module.
  6. 6
    Command the valve on with a scan tool while monitoring amperage to confirm driver operation.
  7. 7
    Replace the injection valve if coil resistance is out of specification after confirming circuit integrity.

Vehicles where we've handled P29AE

Platforms in our catalogue with confirmed P29AE coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Will this code cause a speed limiter?

Yes. Most emissions-regulated vehicles derate engine power or impose a speed limit after the SCR system has been non-functional for a regulatory number of drive cycles.

Can frozen DEF cause this code?

A seized valve due to frozen DEF can prevent normal electrical operation; allow the DEF system to thaw completely before electrical testing.

How is Bank 1 defined for the reductant system?

Bank 1 refers to the cylinder bank containing cylinder number one; on inline engines there is only one bank, so Bank 1 designates the primary SCR dosing injector.

Is the control module likely to blame?

Module failure is uncommon. Exhaust heat and moisture cause the majority of failures in the wiring and connector, which should be fully tested first.

Disabling P29AE in software

RaceTune can permanently disable P29AE — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECUs with a P29AE disable in our catalogue

Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.

  • Bosch EDC17C50 verified 1 software version

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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