EN

Severity: Low Code type: Generic (all makes)

P0670 Code: Glow Plug Control Module Circuit

The engine computer can't properly control or hear back from the diesel's glow plug control module.

At a glance

Severity: 2/5 – Low2/5

Severity: Low

Meaning
Glow Plug Control Module Circuit
System
Ignition & Misfire · Powertrain
Safe to drive?
Yes, short term
Typical repair cost
$60–$2,000
DIY difficulty
Moderate

Many diesels don't switch their glow plugs with a simple relay. They use a glow plug control module, which takes a command from the engine computer, powers each plug individually, often pulsing the current, and reports faults back. P0670 means the engine computer has found a problem in that link: the command circuit, the module's diagnostic or data line, or the module's own power supply and ground. The module sits between a heavy battery feed and the plugs, so it has to cope with high current, heat and, on some vehicles, road spray. When it fails, often several or all plugs stop heating at once, and cylinder glow plug codes may be stored alongside P0670.

Can I keep driving? The engine runs normally once started, so you can drive. Cold starts below about 40 °F will be slow and smoky. If the battery keeps going flat, disconnect the module's main feed until it's repaired, because a module stuck on can drain it and overheat the plugs.

How to read P0670

How to read P0670P10263704
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 6 Computer & outputs
  4. 70 Specific fault

Symptoms

  • Hard starting and heavy white smoke on cold mornings
  • Several glow plug codes at once, or a module code alone
  • Wait-to-start light behaves oddly: stays on, flashes or skips its normal cycle
  • Rough, knocking idle for the first minutes after a cold start
  • Battery drained overnight in some failure modes

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Glow plug control module failed internally, from heat, water or corrosion 32%
  2. Corroded or loose module connector, especially on modules mounted low or on the frame 18%
  3. Module main power feed, fusible link or ground connection faulty 16%
  4. Command or diagnostic wire between engine computer and module open or shorted 14%
  5. Shorted glow plug overloaded a module output and damaged it 12%
  6. Engine computer command driver has failed 8%

Diagnosis step by step

Diagnostic flow: P06701Read every code and note the pattern2Find and inspect the module3Check power and ground under load4Check the command and feedbacksignals5Measure the plugs before fitting anew module6Fit, code if needed and verify

  1. Read every code and note the pattern

    P0670 with codes for several cylinders points to the module or its supply. P0670 alone points to the link between computer and module. Also look for low-voltage codes, because a weak battery can upset the module during its high-current glow cycle.

    Tools: OBD-II scanner

  2. Find and inspect the module

    Its location varies widely: on the frame rail, near the battery, on the intake manifold or low in the engine bay. Look for a cracked case, green corrosion in the connector and chafed wires. Modules mounted where road spray reaches them often fail from water in the connector.

    Tools: Flashlight, Screwdriver

  3. Check power and ground under load

    Measure the heavy feed at the module: battery voltage with the key off, and no more than about half a volt lower during a glow cycle. Then measure the ground from module case or ground pin to the battery negative post during glow: more than about 0.2 volt means a poor ground.

    Tools: Multimeter

  4. Check the command and feedback signals

    With a cold engine and the key on, the computer's enable or command wire should change state or pulse during the glow period, and on data-linked modules the line should show activity rather than a flat 0 or 12 volts. A command that arrives while the module does nothing, with good power and ground, condemns the module.

    Tools: Multimeter, OBD-II scanner

  5. Measure the plugs before fitting a new module

    Measure each glow plug from the module connector end, so the harness is included. A plug or wire that reads close to zero ohms, or is shorted to ground, will destroy the new module's output. Replace any shorted plug first.

    Tools: Multimeter

  6. Fit, code if needed and verify

    Some modules must be coded or matched to the engine computer with a dealer-level scan tool after replacement. Seal the connector with the correct grease if the maker specifies it, clear the codes and confirm a normal glow cycle on the next cold start.

    Tools: OBD-II scanner, Torque wrench

Where the parts are

Charging system and control modules – P06701234567
Charging system and control modules
  1. 1Battery
  2. 2Alternator
  3. 3Engine computer (ECM)
  4. 4CAN bus
  5. 5Transmission
  6. 6Wheel speed sensor
  7. 7High-voltage battery

Repair options & costs

RepairDIY?Estimated cost
Replace glow plug control module Yes $200–$650
Repair module connector or pigtail No $80–$250
Repair module power feed, fusible link or ground No $60–$250
Replace glow plugs that shorted the module (per plug, normal removal) No $60–$180
Replace engine computer (rare) No $800–$2,000

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Ford

On the 6.0L Power Stroke in Super Duty trucks and the E-Series, the glow plug control module is mounted on the driver-side frame rail, where water and road salt reach it. Module failures and corroded connectors there are a well-known cause of P0670 and multiple glow plug codes, often together with worn glow plug connectors under the valve covers.

Emissions / smog test impact

Depends

Glow plug module faults matter for inspection only where diesels are tested and the fault turns on the check-engine light. Many states exempt diesels or heavier pickups, so check your state's program. Where OBD tests apply, a lit check-engine light fails.

Frequently asked questions

What does a glow plug control module do that a relay doesn't?

A relay simply connects all plugs to the battery. A module powers each plug separately, often pulses the current to hold an exact temperature, keeps the plugs glowing after start for cleaner running, and reports individual plug faults to the engine computer.

Will a new module fix my hard starts?

Only if the module was the fault. Measure the plugs and wiring first. A shorted plug often kills the module, and it will kill a new one too if it isn't replaced.

Can I drive with P0670 in the summer?

Yes. In warm weather a diesel starts with little or no glow. The code usually becomes noticeable at the first frost, so fix it before then, and watch the battery in case the module is draining it.

Does the new module need programming?

On some vehicles, yes. Many European diesels and some pickups expect the module to be coded or matched to the engine computer. Check this before buying, since a used module from another vehicle may not work.

Sources